The Outbound Payments Service listens to the response topic defined in its Postings API Client resource; this is integration.outbound_payments.responses. It receives a message containing a newly-created pb.PostingInstructionBatch resource. The pb.PostingInstructionBatch contains a single instruction of type OutboundHardSettlement which commits two postings:
José's account has been debited 24 EUR
Speedier Payment's internal account has been credited 24 EUR
The debit and credit both affect the DEFAULT address in the COMMITTED posting phase, and use the COMMERCIAL_BANK_MONEY asset class.