I had a similar problem recently which is “ERROR 403 – FORBIDDEN”,
I couldn’t access to the admin panel (back-end)
to fix the problem:
1- Go to cPanel
2- open file manager
3- go to the wp-admin directory
4- open .htaccess file
You may found something similar to this script:
<FilesMatch “.*\.(phtml|php|PhP|php5|suspected)$”>
Order Allow,Deny
Deny from all
</FilesMatch>
change Deny from all
to
Allow from all
