It seems to be a Microsoft problem, if they work with a OpenSSL version lower than 3.5 and osTicket environment with OpenSSL 3.5 or higher.
It's no osTicket problem or IONOS problem...
The problem seems to be the OpenSSL version 3.5.5. (for example in Debian 13 now) This version changes the list of default TLS Groups and added X25519MLKEM768 to the list for Post-quantum protection.
This may cause the problem.
Same problem is reported for nextcloud an explained in this post:
https://github.com/nextcloud/docker/issues/2560#issuecomment-4418929488
now we can set in the plugin:
curl_setopt_array($curl, [
CURLOPT_SSL_EC_CURVES =>
'X25519:secp256r1:X448:secp384r1:secp521r1',
]);
to disable the new list.
this should solve the problem between this OpenSSL versions.
Better solution is, to talk with MS to update their OpenSSL version to 3.5 or newer.
I suggest making no changes to the plugin. At least, no permanent ones.
It is surely only a matter of time before MS uses the new version of OpenSSL...
