Once the payment is recorded, you can send the receipt to the customer. To do so:

Ensure that you configure the payment gateways in the correct Zoho Invoice/Books organization. You can navigate to the Zoho Invoice/Books organization by clicking on the Organization ID in Setup > Billing > Setup in FSM.
To make a payment, the customer will have to do the following from the invoice email or the invoice link:
Using Invoice Credits
Any excess amount paid by the customer (i.e. the amount that is not used to record payment for the invoices) will be available as invoice credits in Zoho FSM. These can be used later while recording invoice payment.
In Zoho Books/Invoice, record the excess payment made by the customer. To do so:
- Navigate to Sales > Payments Received and click New.
- In the Customer Name field, select the customer for whom you want to record the excess payment and in the Amount Received field, enter the amount. Click Save.
If there unpaid invoices present for this customer, a popover (Would you like this amount to be reflected in the Payment field?) will be shown. Click No for this amount to be considered as an excess payment.

- Click Continue to Save.

This excess payment will be available as credits when you try to record payment for an invoice for this customer. To use the credits in Zoho FSM:
- Select the Invoices module from the Work Order Management menu and click the invoice you want to record the payment for.
- Click Apply Now in the Available Credits section displayed on top.

- Enter the amount you want to use from the credits and click Apply Credits.

You can either use the credits to record the payment of the full invoice amount or a part of the invoice amount. After you use the credits to record the payment of only a part of the invoice amount, you can proceed to
record the payment of the remaining amount.