On your PHP Language can not be execute header function, 

header("Location: https://www.thelinuxfaq.com/login.html");exit;}

You need to check your php.ini file, "output_buffering" must be "On" or set the  maximum number of bytes
# vim /usr/lib/php.ini
# vim /etc/php.ini

; Output buffering allows you to send header lines (including cookies) even
; after you send body content, at the price of slowing PHP's output layer a
; bit.  You can enable output buffering during runtime by calling the output
; buffering functions.  You can also enable output buffering for all files by
; setting this directive to On.  If you wish to limit the size of the buffer
; to a certain size - you can use a maximum number of bytes instead of 'On', as
; a value for this directive (e.g., output_buffering=4096).
output_buffering = Off

output_buffering = On


Make sure that the URL has http:// at the beginning of it, or the URL thinks and it going to a path on your domain. So the URL not redirect to an actual site or Link.

Also, can be configure the output_buffering in user root path using suPHP_ConfigPath. Create a .htaccess file and allow user permission

suPHP_ConfigPath /home/username/public_html

Then, create a php.ini file and add the below lines :

output_buffering = On

Finally save it.