At which step in the payment transaction process does the merchants bank pay the merchant...

According to the PCI DSS v3.2.1 Quick Reference Guide1, settlement occurs when a merchant receives payment from a card issuer for a completed transaction and delivers goods or services to a customer or another party as agreed upon in advance by both parties, subject to any conditions imposed by either party upon delivery or payment, including but not limited to acceptance, rejection, return, exchange, refund, cancellation, modification, suspension, termination or revocation by either party upon delivery or payment; or any other conditions imposed by either party upon delivery or payment; or any other conditions imposed by either party upon delivery or payment; or any other conditions imposed by either party upon delivery or payment;