Discover How to Install Bookstack on Portainer! 
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It doesnt work cuz there is an error after deployment.
Oops! An Error Occurred
The server returned a “500 Internal Server Error”.
Something is broken. Please let us know what you were doing when this error occurred. We will fix it as soon as possible. Sorry for any inconvenience caused."
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I have changed APP_KEY. all the rest is by default in compsoe file - as u set.
Can you look for any errors in the logs?
i used portainer to fetch logs. The issue was with user permissions UID GUID 
Our company is using opensuse(sles) so its customized a bit. Wasnt aware of that.