Why do you get Server error 500 on wordprrss

The most possible reasons for this issue are plug-ins  and theme funtion file php errors 

Follow these steps
Deactivate all plugins that you have installed
If you edit theme function php file replace with original php file
Rename .haccsses file
Increase the php memory limit
Upload WordPress core files
Wp-admin wo-includes
Imfrom to your hosting provider