One of the sites was having this error message after I migrated it from one host to another, stating that
The site is currently unable to handle this request
HTTP error 500
Here is what you could try if you were encountering the same error.
Check the error log
If you have the access to the server, the first thing you should check is the error log from the following folder.
Most likely, you will find the exact cause of the problem. By checking the error log, I was able to pin down which plugin and theme were causing the issue.
Disable all plugins
If you can still access the wp-admin dashboard, disable all plugins you have installed and see if your site comes back.
If don’t, you can still disable all plugins by logging into the site via FTP and renaming the plugins folder to something else.
If the site comes back after all plugins were disabled, great. Now, let’s enable them back one-by-one to find which plugin was responsible for the problem
If the site still remains the same unable to handle the request, let’s move to the next step.
Disable the active theme
If you have a custom theme for your site, disable it by renaming the theme folder and see if it brings the site back.
If the theme is a child theme based on another theme, let’s disable or delete the parent theme and see if it helps.
If you are just using a theme out of the box, let’s disable it to see if the site works in the default theme.
By now, you have a great chance bring the site back. If not, let’s leave the comments below with more details.
As a bonus note, the problem I had was the parent theme that is incompatible with PHP 7.0. I ended up using an early version that works.