1. Click Customers, click the the required customer then click Activity.
2. Select the invoice (SI) you want to unallocate then click Unallocate transaction and click Yes.
   
   If the option is disabled, find out why you can't unallocate a transaction.

If you unallocate a receipt from an invoice, the value remains on the customer's account as a payment on account, transaction type - SA.

 

[BCB:19:UK - Sales message :ECB]