referral to another site after making an appointment on afacuityscheduling

Hello, I need to make a referral to another site (a payment site for that matter since the options offered by acuityscheduling do not work with my country) after making an appointment.
In the past it was possible to do this with HTML code in Custom Conversion Tracking but for some reason it no longer works for me.
I also have no problem with the Complete Appointment » button going straight to the desired page.
Or even create another new button if possible under Complete Appointment »
What are my options? Thanks for the helpers.