Reply To: Hi. Submit form on the same page where button placed if paid successfully.

The plugin needs a thank you page where the payment processing happens. You can specify a custom Thank You page URL for each of your product. This will make it so the customer gets sent to the page you specify after they pay for that product.

In your case you can use the URL of the page where you have the form that the user should submit after the payment. So the user pays for the product and gets sent to the page where the form is.

If you read the following documentation, it will explain the feature:

Customize the Thank You Page URL and Message of the Stripe Payments Plugin