[0.16.51] Linux headless server uses mods, but client won´t show

[xSniip3Zz]

Hello fellas,
I just installed some mods on my headless server and creating a new map with those mods via command line works fine, but somehow the my client says that my server just juses the base mod and nothing else. Loading a premade save on the server, that requires those mods work, but the client also sais it only uses the base mod. Connecting to the mod save without mods works, but obviously all mod objects disappear.
I tried putting the mods into the mods folder, as well as into the data folder zipped and unzipped but nothing works.

I hope you can help me.

Kind regards
xSniip3Zz