How to fix Error while displaying webpage after a purchase

If you're getting the error:

"Order successfully placed!

However, Something went wrong while displaying this webpage, please contact the seller."

Here's how to fix:

This error is shown because the order form tries to send the customer to the next page in the funnel / website, but there is no next page to display. You can add a next page to fix this issue, or change the redirect action on the order form settings.