Based on the docs of a web billing paywall + custom success page, it looks like the app_user_id URL param is automatically appended. However, I am not seeing this when testing...the sandbox URL maybe does not know the different of environments, so the ID does not get passed back to complete the test?
Is this an issue because I am using a custom paywall also?
I am now nervous to launch my renewal subscription to 2k users. I tested on production too, with the same outcome. How can I get the app_user_id?
