Change data directory after created container

Hello together!

I have a problem where I do not know what to do. I have created a nextcloud docker container and a volume pointing to /var/www/html.

Everything works very well! Now I wanted to mount my NAS which already contains data (is also mounted). As soon as I reconfigure the Docker container, I get an error message on the website with the following content.

Internal Server Error

The server encountered an internal error and was unable to complete your request.
Please contact the server administrator if this error reappears multiple times, please include the technical details below in your report.
More details can be found in the server log.

The volumes look like this

#      - nextcloud-data-folder:/var/www/html
      - /mnt/nas/foldername/data:/var/www/html/data

I have no idea what i’m doing wrong…would love to get some help here :)!

Thanks a lot!