I was so frustrated with this issue and think I finally figured out how to do it.
To recap, the issue is that a bill was paid in full, and it's discovered that the supplier needs to issue a refund. A supplier credit is created, and the money has been refunded in the bank. However, in the bank feed it's not possible to match the deposited amount showing in the bank feed to the o/s supplier credit.
Once a supplier credit is created, it needs to be linked to a bank deposit, and then these two need to be offset against one another through a cheque payment.
Here's a good forum that explains all of the above:
https://quickbooks.intuit.com/learn-support/en-ca/pay-bills/how-do-i-handle-supplier-credits-and-ref...
