Error in the website

when i am trying to login admin it shows Warning: Use of undefined constant REQUEST_URI – assumed ‘REQUEST_URI’ (this will throw an Error in a future version of PHP) in /srv/users/serverpilot/apps/funnyguru/public/wp-content/themes/bimber/functions.php on line 73 Warning: Cannot modify header information – headers already sent by (output started at /srv/users/serverpilot/apps/funnyguru/public/wp-content/themes/bimber/functions.php:73) in /srv/users/serverpilot/apps/funnyguru/public/wp-includes/pluggable.php on line 1219 what should i do?? Is there any error in the theme i purchased a paid theme? here is the link