A sales invoice is prepared from the proforma invoice in order to reflect the prepayment on the sales invoice, in order that the transaction data would be reflected in SimplBooks VAT reports.
More information on preparing a prepayment sales invoice can be found here: Proforma invoice
1. In the prepayment view click on the Prepare a sales invoice from a proforma invoice button under OPERATIONS.
2. When preparing a sales invoice from a proforma invoice, the receipts related to the proforma invoice are automatically taken into account.
Check and save.