Reply To: Can't activate Max2Play License on v2.50

Solution:

While I first thought ShairTunes2 LMS plugin might have played a role, my understanding now is that Php comes with its own version of openSSL.

Stack Overflow reveals that the error in many cases is triggered by a missing certificate.
While trying to download the recommended certificate I encountered something strange:

$ wget https://curl.haxx.se/ca/cacert.pem
--2019-07-15 22:35:35--  https://curl.haxx.se/ca/cacert.pem
Resolving curl.haxx.se (curl.haxx.se)... 151.101.130.49, 151.101.194.49, 151.101.2.49, ...
Connecting to curl.haxx.se (curl.haxx.se)|151.101.130.49|:443... connected.
ERROR: The certificate of ‘curl.haxx.se’ is not trusted.
ERROR: The certificate of ‘curl.haxx.se’ hasn't got a known issuer.

Turns out, the certificate store (here /etc/ssl/certs) was empty.
Luckily on Debian the solution is trivial:
sudo apt-get install ca-certificates

Source: https://stackoverflow.com/questions/9224298/how-do-i-fix-certificate-errors-when-running-wget-on-an-https-url-in-cygwin

I can’t exclude the possibility that something else cleared the certificate store (couldn’t say what did), however, I strongly suggest to check your upgrade scripts.