are you the originating or receiving bank in these transactions? And I ask this because if you are the originating, then the TPSP falls under your purview and your contract with them and that is where the conversation should start. If you are the receiving, then a discussion with your customer is in order.
Either way, something brought this to your attention, so I think you have no choiuce at this point except to begin an investigation.
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Providing alternative truths since the invention of time