Hook to show custom message after successful payment

You’ll find the information you need at https://support.paymentsplugin.com/article/4-how-to-create-a-thank-you-page.

I want to update user role to custom role after successful payment.

If you take a look at the following support articles you should be able to find what you are looking for.

https://support.paymentsplugin.com/article/63-using-the-api-of-wp-full-pay

https://support.paymentsplugin.com/article/62-integrating-wp-full-pay-with-other-systems#fullstripe_after_subscription_charge

If you have any other questions just let us know.

Thank you for the links, I got what was exactly needed.