From PhpCOIN Documentation
To apply a payment to an invoice, display the invoice on-screen then click the [Payment] link at the bottom of the invoice.
Enter the details of the payment, whether it is a full payment or a partial payment. phpCOIN will calculate and display the balance due on the invoice, and also automatically enter this as the payment amount.
- If this payment is for less than the balance due, simply over-ride the payment amount ~ phpCOIN will automatically update the balance due.
- If this payment will pay the invoice in full, click "Set parent invoice to paid".
If you want phpCOIN to automatically email a payment acknowledgment, also click [Send Transaction Acknowledgement Email]. If you have enabled accepting client with no email address and this particular client does not have an email address, there will be no [Send Transaction Acknowledgement Email] option
When you have completed the payment details, click the [Add] button to process the payment.