Unlike regular sales invoices, you cannot unallocate quick entries from the quick entries area. Instead, you must unallocate from the customer receipt. 

Once you unallocate your transactions, the sales quick entry invoice becomes outstanding and your customer receipt shows as a payment on account.

Unallocate from the customer receipt

1. From Banking, open the bank account with the allocated receipt.
2. Find the customer receipt in the bank Activity.
3. Select the Customer Receipt to open its details.
4. Untick the checkbox on the invoice you want to unallocate. The transaction type on the quick entry invoice shows QE-Inv.
5. Select Save, then from the Confirm window select Yes to save the unallocated amount as a payment on account.

Unallocate a customer receipt from a sales invoice