Put SWIFT serial payment (MT103) back in order

THE DRILL AS TEXT

1. In SWIFT serial payment (MT103), what happens first, and what follows?
   • The customer orders a USD transfer abroad — The ordering customer instructs Bank Alfa to pay a supplier banked at Cassia Bank in another country. Bank Alfa has no direct account relationship with Cassia — that is why correspondents exist.
   • Bank Alfa validates and screens — Format and balance checks plus sanctions screening. Cross-border payments face stricter screening because more jurisdictions are involved.
   • The customer's account is debited — Bank Alfa books the debit and, per the charge option, any fees.
   • The MT103 goes to Bank Alfa's USD correspondent — In the serial method the payment instruction itself travels through the account chain. Meridian holds Bank Alfa's USD account (Bank Alfa's nostro), so Meridian can debit it.
   • Meridian validates and screens in the middle — Every bank in the chain screens independently. Meridian also checks that Bank Alfa's account has cover for the debit.
   • Money moves across the books of Meridian — Both Bank Alfa and Cassia hold USD accounts at Meridian. Settlement here is a book transfer in commercial bank money: Meridian debits one account it holds and credits the other.