Pro sites checkout page mixed content in form

I'm having issue with mixed content in form action in pro sites in payment gateway form. i have no idea where to change the form action to http.

Error in console:
Mixed Content: The page at 'https://mysite.com/pro-site/' was loaded over a secure connection, but contains a form that targets an insecure endpoint 'http://mysite.com/pro-site/'. This endpoint should be made available over a secure connection.