From RocKPOS version 4.1.10, we added the "Pre-order" block on the Sell page to help you pay for the pre-order quickly.
Take an example: you had an order. Its reference is NEZIJOSMR.
Step 1: Click the Pre-order block
Step 2: Search its reference, ID, or customer's name. I take its reference in this example.
Step 3: Click "Pay" button
Step 4: Input the amount to pay
Step 5: Select payment methods to complete
And payment completed!