Final answer:
Peter advises that store associates should always provide the transaction ID when searching for a payment not showing in the POS system, as it is vital for tracking down the specific transaction.
Step-by-step explanation:
When calling in to search for a payment that is not showing in the Point of Sale (POS) system, Peter suggested to always have the store associate provide the transaction ID.
This identifier is crucial as it uniquely represents the transaction within the system and will help track down the specific payment.
Restarting the POS system, rebooting the payment terminal, or clearing the payment cache might be troubleshooting steps for different issues, but for locating a specific transaction, the transaction ID is essential.