The provider reported a different amount than the payment

A provider event reported success for an amount that is not the payment's amount. paygate deliberately does not transition the payment: it records the attempt result and emits PaymentAmountMismatch so a human decides.

What to do

Nothing automatic. Do not mark the order paid and do not refund on your side. The payment stays where it was and the mismatch appears as an exception in the dashboard for operations to resolve — usually a partial capture or a provider-side fee deduction. If you see this regularly for one method, the amount you send and the amount the payer is charged are diverging somewhere in your checkout, which is worth finding.