- Protect Content - Does sandbox testing have the same requirement of SSL cert?

This is just a test site that I'm working with to learn more about Protect Content - The signup goes smooth and I believe that the majority of the entire process is set up. I have sample content placed and protected.
I'm using my sandbox for testing. I have double and triple checked that the api's id and key are correct.
Issue - when I click the payment button I am just instantly placed on a 404 page. Not action recorded at all on the sandbox.

Surely I'm just missing a simple step here.

Many Thanks in advance and I really appreciate the level of support in my experience so far!

Support Access is granted and I will be monitoring this as closely as possible.

Thank You and Hope that You are all having a great day out there!