How do I allocate a payment received from customer into the bank to a sales recipt?

Hello Sara162, 

Welcome to the Community page, 

So you can either just add as a sales receipt on the banking page my clicking on the transaction> on transaction type selecting sales receipt> fill the rest of the information in > the click on add or you can create a sales receipt and as long as the date, amount and account is the same it should bring it up as a match on the banking page for you to then select.