Absolutely no settings/code have changed, this all worked 1 week ago (used exact same buyer login to perform test subscription and it worked), now I'm getting following error:
I have checked the seller account settings and "block non-encrypted payment URLs" setting is turned OFF. (found some google posts suggesting to check this).
Any help greatly appreciated, as you can see PayPal's error is not very helpful in helping to diagnose the problem.
This is (almost certainly) an issue on PayPal's side.
We're seeing the same error on our end, without code changes either.
Unfortunately, the status page doesn't mention this incident at the moment (2022-02-01 15:00:00 UTC):
https://www.paypal-status.com/product/sandbox
Check that page regularly over the next few hours, as well as the "Incident history" page:
https://www.paypal-status.com/history/sandbox