Hi, @sunilwriteup

I will recommend you to check the PHP error_log and see if there are any logged errors when you try to enter the backend. You can create a phpinfo file and see if the error logging is enabled and the exact location of the error_log and then you can simply tail the log and then try to access the admin area.

The phpinfo.php file should have the following content:

<?php
phpinfo();
?>

You can also check this via the command line using this command:

php -i | grep error_log

The file can be placed in the public_html folder of the site and then you can access the file in your browser: mydomain.com/phpinfo.php

Then you can check for the following values:

log_errors –> Make sure this is set to On

error_log

If you need to install or update a plugin you can also use wp-cli to do this via the command line:

https://www.digitalocean.com/community/tutorials/how-to-use-wp-cli-to-manage-your-wordpress-site-from-the-command-line

Hope that helps!

Regards,
Alex