I have allocated payments made to a supplier to Creditors as we had not received their invoice. We have now received the invoice how do I match those payments to invoice

You can match the payment by going to the Pay Bills menu and selecting the invoice that you received from your supplier, sarah162. I'll provide the detailed steps below.

1. Go to the + New button and select Pay bills.
2. From the Payment account dropdown, choose the specific payment account.
3. Tick the checkbox for the invoice transaction you wish to pay, and the credits will show under the Credit Applied column.
   
   
   
   
4. Once done, select Save and close.

I've included an article for you to browse for assistance with managing bills that need to be reimbursed now or later, whether using bills, checks, or tracking expenses: Learn the difference between bills, checks, and expenses in QuickBooks Online. 

Stay in touch if you need additional assistance managing bill payments in QBO. The Community is available anytime to answer your questions.