We correctly set the return URL to ap_returnurl as their API requires. The return URL however is likely not the issue. It's that the crypt check is failing. Install latest CBSubs and latest Payza gateway then try the following.

IPN Status: Enabled
Enable IPN Version 2: Enabled
Allow Encrypted Payment Details (EPD): Enabled
Enable EPD Version 2: Disabled

Looks like we added support for v2 IPN, but I don't see handling for EPD v2. I don't know what else to suggest. As explained already their change to test center prevents me from even testing the gateway integration now.

I am not providing my entire life worth of personal details to test an integration; that is not acceptable. Contact Payza if you'd like them to reverse their ridiculous test center changes otherwise there's nothing more I can do. I can't even contact their support without giving date of birth and the name of my internet service provider (why would either even be remotely relevant). The amount of information they keep asking for is absolutely ridiculous.

I suggest maybe looking into using one of the other gateways we provide. We've just released a Stripe gateway integration.

That is not how CBSubs works. It's not that simple. You can not just add a payment button via the HTML and expect it to properly pay the subscription in CBSubs. I again highly recommend reviewing changing gateways or contacting Payza to see what is going on with their test center and why developer accounts are required to provide such an absurd amount of information. As it stands our support for Payza is on hold until we can get such issues worked out.

Your best option in that case is to setup an Offline payment gateway then specify the HTML for your payment button as part of the offline payment slip display.