500 – Internal server error on all of website

hi,
I’m getting a 500 error on my entire webiste: https://www.masteremergencyarchitecture.com

On Friday I uploaded a Coauthors Plugin and tweaked the author tags to this effect, and everything was working perfectly. As of Sunday afternoon, the website is down and I cannot access any part of it.

I have looked through similar threads on this problem and have tried to lower the permissions on my www file via ftp, but it doesn’t let me change any permissions whatsoever. I’m worried that it could have something to do with the fact that I have added new users (as contributors) who will be authoring posts in addition to me, the admin. They only have contributor permissions though.

I have no idea what’s happened!! Please please help me.

thank you