What should I ask my customer for when an ACH payment needs tracing?

Ask for the bank's final ACH transfer confirmation, not just the original payment request. It should identify the sender, destination, amount, currency and payment date. Ask the payer's bank for its ACH trace or reference number if that is not visible on the receipt.

Send that record to Support together with your invoice and the local USD instructions the customer used. Explain whether the bank shows the payment as pending, completed or failed.

Do not ask for a SWIFT MT103 for an ACH payment. The transfer method determines the tracing record. If the bank says it actually sent a wire rather than ACH, tell Support and use the evidence for the method really used.