Solution:
Glad you sorted your error with incompatible PHP versions.
In order to properly debug an HTTP 500 error, you should do the following.
In your php.ini, set error_reporting to -1
Turn display_errors off
Set a custom error_log path.
Then in your terminal, type tail -f /path/to/error_log.
Now as you work on your project, you can go into your terminal and you will see all notices, warnings, deprecation messages, and fatal error messages, scrolling past in real time.
Then you can tighten the screws. An empty log means well written code!