Database schema for one-to-one and group chat
<p>I am developing API's for chat application that has one-to-one and group chat based on invite. e.g I want to chat with someone first message that i am gonna send him will go as a invite after accepting invitation they can chat and add other users in chat [Group chat]. I am little conscious about minimum tables. The database that i am using now is not fulfilling  my needs. Here is image that shows my current DB. 
<a href="https://i.stack.imgur.com/Jpaqs.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Jpaqs.png" alt="Here is the current schema "></a>
Suggest me some changes or any other options.</p>

<p>Thanks</p>