Hello Lisa,
Before proceeding, could you confirm whether the payment was manually recorded in QuickBooks?
If so, please note that QuickBooks Online (QBO) serves as a bookkeeping tool for tracking transactions. It doesn't facilitate direct payments to suppliers. Here's an article that explains how to locate supplier payments based on their recording method: Learn the difference between bills, cheques, and expenses.
For payments made outside QuickBooks with a linked bank account, navigate to the Bank transactions page in QBO to locate the transaction. When a payment shows in the transaction feed, it confirms successful processing. In such a case, the supplier has to follow up with their bank to ensure the funds are received.
For unlinked accounts, review your bank statements directly to find the payment details.
Let me know if you have other questions or if you meant something different.