Warning Error on WPLMS Setup Wizard

Hello Support, Just bought your theme, started the WP install, and I get this warning error on the configuration check screen : Warning: Cannot modify header information - headers already sent by (output started at /homepages/39/d739436798/htdocs/mooc-elsan/wp-config.php:1) in .../htdocs/mooc-elsan/wp-admin/includes/misc.php on line 1126 But I can pass the screen, untill I select the features and try to "Continue" and I get this blocking error : Warning: Cannot modify header information - headers already sent by (output started at /homepages/39/d739436798/htdocs/mooc-elsan/wp-config.php:1) in .../htdocs/mooc-elsan/wp-includes/pluggable.php on line 1219 My server is in PHP 7.2 Dedicated server... @ 1and1 I need to send a DEMO of the theme to my client by Friday, I hope it will be installed by then... Please come back to me asap, I need to start working on the theme right away. Many thanks