Where do I see the UPI transaction ID my customer entered after paying?

Open the order from Orders → Manage Orders. If the customer submitted proof, a Payment proof card appears on the order page showing:

• Reference: the UTR or transaction ID they typed
• the amount they say they paid, any screenshot, their note and the date

Check that reference against your bank or UPI app. If it matches, click Approve (mark paid). The order moves to Processing and is recorded as paid. If it doesn't match, click Reject, type a reason, for example that the amount is wrong, and click Reject proof. Rejecting cancels the order.