Add a Sales Order Column on Customer Payment Window that will Display the Sales Order Number in which the Invoice to be Paid has been Created from

1. Navigate to Customization > Lists, Records, & Fields > Transaction Body Fields > New
2. Enter the Label of the field.
3. Uncheck the Store Value checkbox.
4. Check the Sale checkbox on the Applies To tab.
5. Click on the Sourcing & Filtering tab.
6. Set the Source List field to Created From.
7. Set the Source From field to Ref. No..
8. Save.
9. Navigate to Transactions > Customers > Accept Customer Payments
10. Click on the Customize button on the Apply > Invoice sub tab.
11. Check the check box of the custom transaction body field created in steps 1-8.
12. Save.
13. Select a customer with invoices to be paid.
 
Result: The sales order number shows up under the new column.