Sending a Thank You Note for Payment is really simple. Navigate to Settings > Email Templates and click on “Thank You Note for Payment”
Click the template and customise the email content if required.
You will notice a checkbox called “Email a ‘Thank you’ note for this payment” while recording a payment on an invoice or when create a payment from the Payments page.
You can also enable a Thank You note to be sent to your customer automatically if they pay online via PayPal. Simply navigate to Settings > Online Payments and click your PayPal payment provider and check the “Send Payments Thanks” checkbox.