The question is: How do i insert the variable (echo $url_endpoint;) as a part of the link in the last line: header(\'Location: http://linkhere.com/HERE_I_WANT_THE_VARIABLE\');
There's nothing here explaining the use of multiple variables, so I'll chuck it in just incase someone needs it in the future.
You need to concatenate multiple variables:
header('Location: http://linkhere.com?var1='.$var1.'&var2='.$var2.'&var3'.$var3);