Build the mandatory GrpHdr, PmtInf, and CdtTrfTxInf blocks of an ISO 20022 pain.001.001.09 message and batch multiple transactions per debtor account correctly

Steps

1. Populate the Group Header (GrpHdr) once per message with a message identification, creation date-time, and the total number and control sum of the individual transactions it carries
2. Create a separate Payment Information (PmtInf) block for each distinct combination of debtor account, requested execution date, and payment method your receiving bank's channel requires, checking that bank's implementation guide since exact batching rules are bank-specific
3. Set the Payment Method element to TRF for credit transfers (as opposed to CHK for cheques) inside each PmtInf block
4. Nest one Credit Transfer Transaction Information (CdtTrfTxInf) element per transaction inside its PmtInf block, carrying the creditor, creditor agent, amount, and remittance information
5. Set the charge bearer code (e.g. SHAR, DEBT, or CRED) consistently with what your receiving bank expects, since mismatches are a common rejection cause
6. Validate the finished file against your bank's specific pain.001.001.09 implementation guide before submission, since banks layer additional bank-specific restrictions on top of the base ISO schema