Production environment not found - problem

Hello,
I installed my project via zip-file, unpacked on the web-server (which runs php 7.4.33. Project developed on server running php 8.1.26).
I was able to call the production environment and configure the db-connecitons. They passed the test. After I stored the php-timezone, I saved the configuration and it did. There were no incompatible applications (test was run), and the diagnosis showed all fine.
BUT:
when I try to start the application (it is the sec-login.php) I receive the message (in German):
# Produktionsumfeld
Produktionsumgebung nicht gefunden. Bitte wenden Sie sich an den Administrator dieser Umgebung.
{var_str_message_conn}
translated:
production environment
*productions environment not found. Please contact the admin of this environment. *
{var_str_message_conn}

Does anyone know what is going wrong?
(I did the same thing on a second server and all went fine)

Help would be highly appreciated!