no, I haven't solved it so far. Still trying to figure out why it's happening.
Productive System where it's functioning: 3.3.5+ -- simple OK return value, user is enroled
Productive System where it's not functioning 3.4.2+ -- forwarding message as return value, user is not enroled
On Test Server (same web-hoster)
Moodle 3.4.2+ -- simple OK return value, user is enroled.
And that's what strucks me. Server configurations looks for me similar. On one it's working, on the other not.
But on the one where 3.4.2+ is not responding as execpted, when returning to 3.3.5+ it's working.