Problem solved. It was the nodebb-plugin-cash who caused the problem.
After deleting this plugin my NodeBB worked again 🙂
How I can combine the forum with the site as here
Advise me needed steps, please
TBH If it is not immediately obvious to you how something like that is done, you will need to hire someone to do it for you. I suggest email@example.com
The site is calling a gmod API, possibly exclserver, but if you couldn't figure that out on your own, you won't be able to set a site like this up on your own. I suggest reading exclserver documentation. I've never used it, but it appears detailed enough.
I meant how I can combine the site navbar with nodebb.That from the forum it was possible to pass on all tabs of a site
They used a custom theme and added the extra navigation items that way. You can already add custom nav menu items in the ACP.