Solution:
About Rest-API plugins – they don’t touch the .htaccess file.
Do you use any Cache plugin(if yes then try to deactivate they)?
To see why you get a 500 error you need to look at the error logs on your server. Depending on your account type these may or may not be available to you, but your hosting company will be able to see what’s happening.
500 errors can frequently occur with incorrectly configured rewrite rules contained in your “.htaccess” files, so you should probably try removing those from your folders to see if it’s the cause. Keep a backup of those files, of course, you might still need them.
- Re-save permalinks
- Check that your server allows overriding directives with .htaccess.
- Check that your server has mod_rewrite enabled
If it doesn’t help try to disable all plugins and try the procedure again.