6c37871c__11_CCP_Installment_Agreements__If_the_reason_box_states_
[And ...] payment located [Then ...] Transfer credit to correct module. Provide updated information to IAT administrator and request 3856 voucher letter. [If the reason box states:] 
IA Payment Found on Secondary SSN Only and Includes Tax Year
Internal Revenue Manual - 5.4.11 CCP Installment Agreements