Hello there, ymanzo.
The best way to further heck the payments you made via Melio that were not received by your vendors is to contact their Customer Support Team. They'll be able to guide you in tracking the payment. You can get their contact information in our QuickBooks App Store.
We also have vendor reports that you can pull up to know the bills and payments applied to them. Then, you can customize it to show the tracking numbers and other details.
Let me know if you have other questions. Take care and have a good one!
