Consumer groups offsets is not working properly
**Describe the bug**
(A clear and concise description of what the bug is.)


**Set up**
(How do you run the app?)


**Steps to Reproduce**
Steps to reproduce the behavior:

1. 

**Expected behavior**
(A clear and concise description of what you expected to happen)

**Screenshots**
(If applicable, add screenshots to help explain your problem)


**Additional context**
(Add any other context about the problem here)
kafka-ui-api/src/main/java/com/provectus/kafka/ui/controller/ConsumerGroupsController.java kafka-ui-api/src/main/java/com/provectus/kafka/ui/service/OffsetsResetService.java kafka-ui-contract/src/main/resources/swagger/kafka-ui-api.yaml
kafka-ui-api/src/main/java/com/provectus/kafka/ui/controller/ConsumerGroupsController.java kafka-ui-api/src/main/java/com/provectus/kafka/ui/service/OffsetsResetService.java kafka-ui-contract/src/main/resources/swagger/kafka-ui-api.yaml
kafka-ui-api/src/test/java/com/provectus/kafka/ui/service/OffsetsResetServiceTest.java
diff --git a/kafka-ui-api/src/main/java/com/provectus/kafka/ui/controller/ConsumerGroupsController.java b/kafka-ui-api/src/main/java/com/provectus/kafka/ui/controller/ConsumerGroupsController.java
index b0bac49169a..b1437a5e119 100644
--- a/kafka-ui-api/src/main/java/com/provectus/kafka/ui/controller/ConsumerGroupsController.java
+++ b/kafka-ui-api/src/main/java/com/provectus/kafka/ui/controller/ConsumerGroupsController.java
@@ -70,42 +70,45 @@ public Mono<ResponseEntity<Void>> resetConsumerGroupOffsets(String clusterName,
                                                               Mono<ConsumerGroupOffsetsReset>
                                                                   consumerGroupOffsetsReset,
                                                               ServerWebExchange exchange) {
-    return consumerGroupOffsetsReset.map(reset -> {
+    return consumerGroupOffsetsReset.flatMap(reset -> {
       var cluster =
           clustersStorage.getClusterByName(clusterName).orElseThrow(ClusterNotFoundException::new);
 
       switch (reset.getResetType()) {
         case EARLIEST:
-          offsetsResetService
+          return offsetsResetService
               .resetToEarliest(cluster, group, reset.getTopic(), reset.getPartitions());
-          break;
         case LATEST:
-          offsetsResetService
+          return offsetsResetService
               .resetToLatest(cluster, group, reset.getTopic(), reset.getPartitions());
-          break;
         case TIMESTAMP:
           if (reset.getResetToTimestamp() == null) {
-            throw new ValidationException(
-                "resetToTimestamp is required when TIMESTAMP reset type used");
+            return Mono.error(
+                new ValidationException(
+                    "resetToTimestamp is required when TIMESTAMP reset type used"
+                )
+            );
           }
-          offsetsResetService
+          return offsetsResetService
               .resetToTimestamp(cluster, group, reset.getTopic(), reset.getPartitions(),
                   reset.getResetToTimestamp());
-          break;
         case OFFSET:
           if (CollectionUtils.isEmpty(reset.getPartitionsOffsets())) {
-            throw new ValidationException(
-                "partitionsOffsets is required when OFFSET reset type used");
+            return Mono.error(
+                new ValidationException(
+                    "partitionsOffsets is required when OFFSET reset type used"
+                )
+            );
           }
           Map<Integer, Long> offsets = reset.getPartitionsOffsets().stream()
               .collect(toMap(PartitionOffset::getPartition, PartitionOffset::getOffset));
-          offsetsResetService.resetToOffsets(cluster, group, reset.getTopic(), offsets);
-          break;
+          return offsetsResetService.resetToOffsets(cluster, group, reset.getTopic(), offsets);
         default:
-          throw new ValidationException("Unknown resetType " + reset.getResetType());
+          return Mono.error(
+              new ValidationException("Unknown resetType " + reset.getResetType())
+          );
       }
-      return ResponseEntity.ok().build();
-    });
+    }).map(o -> ResponseEntity.ok().build());
   }
 
 }
diff --git a/kafka-ui-api/src/main/java/com/provectus/kafka/ui/service/OffsetsResetService.java b/kafka-ui-api/src/main/java/com/provectus/kafka/ui/service/OffsetsResetService.java
index 73d86cecb31..6420e6d7ec3 100644
--- a/kafka-ui-api/src/main/java/com/provectus/kafka/ui/service/OffsetsResetService.java
+++ b/kafka-ui-api/src/main/java/com/provectus/kafka/ui/service/OffsetsResetService.java
@@ -1,18 +1,19 @@
 package com.provectus.kafka.ui.service;
 
 import static com.google.common.base.Preconditions.checkArgument;
+import static com.provectus.kafka.ui.util.ClusterUtil.toMono;
 import static java.util.stream.Collectors.toMap;
 import static java.util.stream.Collectors.toSet;
 import static org.apache.kafka.common.ConsumerGroupState.DEAD;
 import static org.apache.kafka.common.ConsumerGroupState.EMPTY;
 
-import com.google.common.collect.Sets;
 import com.provectus.kafka.ui.exception.NotFoundException;
 import com.provectus.kafka.ui.exception.ValidationException;
-import com.provectus.kafka.ui.model.InternalConsumerGroup;
 import com.provectus.kafka.ui.model.KafkaCluster;
 import java.util.Collection;
 import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
 import java.util.Map;
 import java.util.Set;
 import lombok.RequiredArgsConstructor;
@@ -24,6 +25,7 @@
 import org.apache.kafka.clients.consumer.OffsetAndTimestamp;
 import org.apache.kafka.common.TopicPartition;
 import org.springframework.stereotype.Component;
+import reactor.core.publisher.Mono;
 
 /**
  * Implementation follows https://cwiki.apache.org/confluence/display/KAFKA/KIP-122%3A+Add+Reset+Consumer+Group+Offsets+tooling
@@ -36,64 +38,88 @@
 public class OffsetsResetService {
 
   private final KafkaService kafkaService;
-
-  public void resetToEarliest(KafkaCluster cluster, String group, String topic,
-                              Collection<Integer> partitions) {
-    checkGroupCondition(cluster, group);
-    try (var consumer = getConsumer(cluster, group)) {
-      var targetPartitions = getTargetPartitions(consumer, topic, partitions);
-      var offsets = consumer.beginningOffsets(targetPartitions);
-      commitOffsets(consumer, offsets);
-    }
+  private final AdminClientService adminClientService;
+
+  public Mono<Map<TopicPartition, OffsetAndMetadata>> resetToEarliest(
+      KafkaCluster cluster, String group, String topic, Collection<Integer> partitions) {
+    return checkGroupCondition(cluster, group)
+        .flatMap(g -> {
+          try (var consumer = getConsumer(cluster, group)) {
+            var targetPartitions = getTargetPartitions(consumer, topic, partitions);
+            var offsets = consumer.beginningOffsets(targetPartitions);
+            return commitOffsets(consumer, offsets);
+          }
+        });
   }
 
-  public void resetToLatest(KafkaCluster cluster, String group, String topic,
-                            Collection<Integer> partitions) {
-    checkGroupCondition(cluster, group);
-    try (var consumer = getConsumer(cluster, group)) {
-      var targetPartitions = getTargetPartitions(consumer, topic, partitions);
-      var offsets = consumer.endOffsets(targetPartitions);
-      commitOffsets(consumer, offsets);
-    }
+  public Mono<Map<TopicPartition, OffsetAndMetadata>> resetToLatest(
+      KafkaCluster cluster, String group, String topic, Collection<Integer> partitions) {
+    return checkGroupCondition(cluster, group).flatMap(
+        g -> {
+          try (var consumer = getConsumer(cluster, group)) {
+            var targetPartitions = getTargetPartitions(consumer, topic, partitions);
+            var offsets = consumer.endOffsets(targetPartitions);
+            return commitOffsets(consumer, offsets);
+          }
+        }
+    );
   }
 
-  public void resetToTimestamp(KafkaCluster cluster, String group, String topic,
-                               Collection<Integer> partitions, long targetTimestamp) {
-    checkGroupCondition(cluster, group);
-    try (var consumer = getConsumer(cluster, group)) {
-      var targetPartitions = getTargetPartitions(consumer, topic, partitions);
-      var offsets = offsetsByTimestamp(consumer, targetPartitions, targetTimestamp);
-      commitOffsets(consumer, offsets);
-    }
+  public Mono<Map<TopicPartition, OffsetAndMetadata>> resetToTimestamp(
+      KafkaCluster cluster, String group, String topic, Collection<Integer> partitions,
+      long targetTimestamp) {
+    return checkGroupCondition(cluster, group).flatMap(
+        g -> {
+          try (var consumer = getConsumer(cluster, group)) {
+            var targetPartitions = getTargetPartitions(consumer, topic, partitions);
+            var offsets = offsetsByTimestamp(consumer, targetPartitions, targetTimestamp);
+            return commitOffsets(consumer, offsets);
+          }
+        }
+    );
   }
 
-  public void resetToOffsets(KafkaCluster cluster, String group, String topic,
-                             Map<Integer, Long> targetOffsets) {
-    checkGroupCondition(cluster, group);
-    try (var consumer = getConsumer(cluster, group)) {
-      var offsets = targetOffsets.entrySet().stream()
-          .collect(toMap(e -> new TopicPartition(topic, e.getKey()), Map.Entry::getValue));
-      offsets = editOffsetsIfNeeded(consumer, offsets);
-      commitOffsets(consumer, offsets);
-    }
+  public Mono<Map<TopicPartition, OffsetAndMetadata>> resetToOffsets(
+      KafkaCluster cluster, String group, String topic, Map<Integer, Long> targetOffsets) {
+    return checkGroupCondition(cluster, group).flatMap(
+        g -> {
+          try (var consumer = getConsumer(cluster, group)) {
+            var offsets = targetOffsets.entrySet().stream()
+                .collect(toMap(e -> new TopicPartition(topic, e.getKey()), Map.Entry::getValue));
+            offsets = editOffsetsIfNeeded(consumer, offsets);
+            return commitOffsets(consumer, offsets);
+          }
+        }
+    );
   }
 
-  private void checkGroupCondition(KafkaCluster cluster, String groupId) {
-    InternalConsumerGroup description =
-        kafkaService.getConsumerGroupsInternal(cluster)
-            .blockOptional()
-            .stream()
-            .flatMap(Collection::stream)
-            .filter(cgd -> cgd.getGroupId().equals(groupId))
-            .findAny()
-            .orElseThrow(() -> new NotFoundException("Consumer group not found"));
-
-    if (!Set.of(DEAD, EMPTY).contains(description.getState())) {
-      throw new ValidationException(
-          String.format(
-              "Group's offsets can be reset only if group is inactive, but group is in %s state",
-              description.getState()));
-    }
+  private Mono<ConsumerGroupDescription> checkGroupCondition(KafkaCluster cluster, String groupId) {
+    return adminClientService.getOrCreateAdminClient(cluster)
+        .flatMap(ac ->
+            // we need to call listConsumerGroups() to check group existence, because
+            // describeConsumerGroups() will return consumer group even if it doesn't exist
+            toMono(ac.getAdminClient().listConsumerGroups().all())
+                .filter(cgs -> cgs.stream().anyMatch(g -> g.groupId().equals(groupId)))
+                .flatMap(cgs -> toMono(
+                    ac.getAdminClient().describeConsumerGroups(List.of(groupId)).all()))
+                .filter(cgs -> cgs.containsKey(groupId))
+                .map(cgs -> cgs.get(groupId))
+                .flatMap(cg -> {
+                  if (!Set.of(DEAD, EMPTY).contains(cg.state())) {
+                    return Mono.error(
+                        new ValidationException(
+                            String.format(
+                                "Group's offsets can be reset only if group is inactive,"
+                                    + " but group is in %s state",
+                                cg.state()
+                            )
+                        )
+                    );
+                  }
+                  return Mono.just(cg);
+                })
+                .switchIfEmpty(Mono.error(new NotFoundException("Consumer group not found")))
+        );
   }
 
   private Map<TopicPartition, Long> offsetsByTimestamp(Consumer<?, ?> consumer,
@@ -107,7 +133,10 @@ private Map<TopicPartition, Long> offsetsByTimestamp(Consumer<?, ?> consumer,
         .collect(toMap(Map.Entry::getKey, e -> e.getValue().offset()));
 
     // for partitions where we didnt find offset by timestamp, we use end offsets
-    foundOffsets.putAll(consumer.endOffsets(Sets.difference(partitions, foundOffsets.keySet())));
+    Set<TopicPartition> endOffsets = new HashSet<>(partitions);
+    endOffsets.removeAll(foundOffsets.keySet());
+    foundOffsets.putAll(consumer.endOffsets(endOffsets));
+
     return foundOffsets;
   }
 
@@ -155,11 +184,13 @@ private Map<TopicPartition, Long> editOffsetsIfNeeded(Consumer<?, ?> consumer,
     return result;
   }
 
-  private void commitOffsets(Consumer<?, ?> consumer, Map<TopicPartition, Long> offsets) {
-    consumer.commitSync(
-        offsets.entrySet().stream()
-            .collect(toMap(Map.Entry::getKey, e -> new OffsetAndMetadata(e.getValue())))
-    );
+  private Mono<Map<TopicPartition, OffsetAndMetadata>> commitOffsets(
+      Consumer<?, ?> consumer, Map<TopicPartition, Long> offsets
+  ) {
+    var toCommit = offsets.entrySet().stream()
+        .collect(toMap(Map.Entry::getKey, e -> new OffsetAndMetadata(e.getValue())));
+    consumer.commitSync(toCommit);
+    return Mono.just(toCommit);
   }
 
   private Consumer<?, ?> getConsumer(KafkaCluster cluster, String groupId) {
diff --git a/kafka-ui-contract/src/main/resources/swagger/kafka-ui-api.yaml b/kafka-ui-contract/src/main/resources/swagger/kafka-ui-api.yaml
index 7f446bdba2d..cb882ef078a 100644
--- a/kafka-ui-contract/src/main/resources/swagger/kafka-ui-api.yaml
+++ b/kafka-ui-contract/src/main/resources/swagger/kafka-ui-api.yaml
@@ -2256,7 +2256,6 @@ components:
           format: int64
       required:
         - partition
-        - offset
 
     ConsumerGroupOffsetsResetType:
       type: string

diff --git a/kafka-ui-api/src/test/java/com/provectus/kafka/ui/service/OffsetsResetServiceTest.java b/kafka-ui-api/src/test/java/com/provectus/kafka/ui/service/OffsetsResetServiceTest.java
index 779bda4d3ea..290cfec9d76 100644
--- a/kafka-ui-api/src/test/java/com/provectus/kafka/ui/service/OffsetsResetServiceTest.java
+++ b/kafka-ui-api/src/test/java/com/provectus/kafka/ui/service/OffsetsResetServiceTest.java
@@ -56,7 +56,7 @@ void init() {
     FeatureService featureService = new FeatureServiceImpl(brokerService);
     adminClientService.setClientTimeout(5_000);
     kafkaService = new KafkaService(null, null, null, null, adminClientService, featureService);
-    offsetsResetService = new OffsetsResetService(kafkaService);
+    offsetsResetService = new OffsetsResetService(kafkaService, adminClientService);
 
     createTopic(new NewTopic(topic, PARTITIONS, (short) 1));
     createConsumerGroup();
@@ -78,17 +78,22 @@ private void createConsumerGroup() {
   @Test
   void failsIfGroupDoesNotExists() {
     assertThatThrownBy(
-        () -> offsetsResetService.resetToEarliest(CLUSTER, "non-existing-group", topic, null))
-        .isInstanceOf(NotFoundException.class);
+        () -> offsetsResetService
+            .resetToEarliest(CLUSTER, "non-existing-group", topic, null).block()
+    ).isInstanceOf(NotFoundException.class);
     assertThatThrownBy(
-        () -> offsetsResetService.resetToLatest(CLUSTER, "non-existing-group", topic, null))
-        .isInstanceOf(NotFoundException.class);
+        () -> offsetsResetService
+            .resetToLatest(CLUSTER, "non-existing-group", topic, null).block()
+    ).isInstanceOf(NotFoundException.class);
     assertThatThrownBy(() -> offsetsResetService
-        .resetToTimestamp(CLUSTER, "non-existing-group", topic, null, System.currentTimeMillis()))
-        .isInstanceOf(NotFoundException.class);
+        .resetToTimestamp(CLUSTER, "non-existing-group", topic, null, System.currentTimeMillis())
+        .block()
+    ).isInstanceOf(NotFoundException.class);
     assertThatThrownBy(
-        () -> offsetsResetService.resetToOffsets(CLUSTER, "non-existing-group", topic, Map.of()))
-        .isInstanceOf(NotFoundException.class);
+        () -> offsetsResetService
+            .resetToOffsets(CLUSTER, "non-existing-group", topic, Map.of())
+            .block()
+    ).isInstanceOf(NotFoundException.class);
   }
 
   @Test
@@ -98,16 +103,19 @@ void failsIfGroupIsActive() {
       consumer.subscribe(Pattern.compile("no-such-topic-pattern"));
       consumer.poll(Duration.ofMillis(100));
 
-      assertThatThrownBy(() -> offsetsResetService.resetToEarliest(CLUSTER, groupId, topic, null))
-          .isInstanceOf(ValidationException.class);
-      assertThatThrownBy(() -> offsetsResetService.resetToLatest(CLUSTER, groupId, topic, null))
-          .isInstanceOf(ValidationException.class);
+      assertThatThrownBy(() ->
+          offsetsResetService.resetToEarliest(CLUSTER, groupId, topic, null).block()
+      ).isInstanceOf(ValidationException.class);
+      assertThatThrownBy(
+          () -> offsetsResetService.resetToLatest(CLUSTER, groupId, topic, null).block()
+      ).isInstanceOf(ValidationException.class);
       assertThatThrownBy(() -> offsetsResetService
-          .resetToTimestamp(CLUSTER, groupId, topic, null, System.currentTimeMillis()))
-          .isInstanceOf(ValidationException.class);
+          .resetToTimestamp(CLUSTER, groupId, topic, null, System.currentTimeMillis())
+          .block()
+      ).isInstanceOf(ValidationException.class);
       assertThatThrownBy(
-          () -> offsetsResetService.resetToOffsets(CLUSTER, groupId, topic, Map.of()))
-          .isInstanceOf(ValidationException.class);
+          () -> offsetsResetService.resetToOffsets(CLUSTER, groupId, topic, Map.of()).block()
+      ).isInstanceOf(ValidationException.class);
     }
   }
 
@@ -116,7 +124,7 @@ void resetToOffsets() {
     sendMsgsToPartition(Map.of(0, 10, 1, 10, 2, 10));
 
     var expectedOffsets = Map.of(0, 5L, 1, 5L, 2, 5L);
-    offsetsResetService.resetToOffsets(CLUSTER, groupId, topic, expectedOffsets);
+    offsetsResetService.resetToOffsets(CLUSTER, groupId, topic, expectedOffsets).block();
     assertOffsets(expectedOffsets);
   }
 
@@ -126,7 +134,7 @@ void resetToOffsetsCommitsEarliestOrLatestOffsetsIfOffsetsBoundsNotValid() {
 
     var offsetsWithInValidBounds = Map.of(0, -2L, 1, 5L, 2, 500L);
     var expectedOffsets = Map.of(0, 0L, 1, 5L, 2, 10L);
-    offsetsResetService.resetToOffsets(CLUSTER, groupId, topic, offsetsWithInValidBounds);
+    offsetsResetService.resetToOffsets(CLUSTER, groupId, topic, offsetsWithInValidBounds).block();
     assertOffsets(expectedOffsets);
   }
 
@@ -135,11 +143,11 @@ void resetToEarliest() {
     sendMsgsToPartition(Map.of(0, 10, 1, 10, 2, 10));
 
     commit(Map.of(0, 5L, 1, 5L, 2, 5L));
-    offsetsResetService.resetToEarliest(CLUSTER, groupId, topic, List.of(0, 1));
+    offsetsResetService.resetToEarliest(CLUSTER, groupId, topic, List.of(0, 1)).block();
     assertOffsets(Map.of(0, 0L, 1, 0L, 2, 5L));
 
     commit(Map.of(0, 5L, 1, 5L, 2, 5L));
-    offsetsResetService.resetToEarliest(CLUSTER, groupId, topic, null);
+    offsetsResetService.resetToEarliest(CLUSTER, groupId, topic, null).block();
     assertOffsets(Map.of(0, 0L, 1, 0L, 2, 0L, 3, 0L, 4, 0L));
   }
 
@@ -148,11 +156,11 @@ void resetToLatest() {
     sendMsgsToPartition(Map.of(0, 10, 1, 10, 2, 10, 3, 10, 4, 10));
 
     commit(Map.of(0, 5L, 1, 5L, 2, 5L));
-    offsetsResetService.resetToLatest(CLUSTER, groupId, topic, List.of(0, 1));
+    offsetsResetService.resetToLatest(CLUSTER, groupId, topic, List.of(0, 1)).block();
     assertOffsets(Map.of(0, 10L, 1, 10L, 2, 5L));
 
     commit(Map.of(0, 5L, 1, 5L, 2, 5L));
-    offsetsResetService.resetToLatest(CLUSTER, groupId, topic, null);
+    offsetsResetService.resetToLatest(CLUSTER, groupId, topic, null).block();
     assertOffsets(Map.of(0, 10L, 1, 10L, 2, 10L, 3, 10L, 4, 10L));
   }
 
@@ -169,7 +177,9 @@ void resetToTimestamp() {
             new ProducerRecord<Bytes, Bytes>(topic, 2, 1100L, null, null),
             new ProducerRecord<Bytes, Bytes>(topic, 2, 1200L, null, null)));
 
-    offsetsResetService.resetToTimestamp(CLUSTER, groupId, topic, List.of(0, 1, 2, 3), 1600L);
+    offsetsResetService.resetToTimestamp(
+        CLUSTER, groupId, topic, List.of(0, 1, 2, 3), 1600L
+    ).block();
     assertOffsets(Map.of(0, 2L, 1, 1L, 2, 3L, 3, 0L));
   }
 
