Can’t add more codes

Try to fix the constant defintions. Described here:
https://www.ads-software.com/support/topic/help-not-compatible-with-php-7-2/

Otherways there your server is running php7.x where the Function split() is removed.
Replace split( with explode( in dc_import_codes() located in includes/helpers/db.php

Or have a look here: https://www.ads-software.com/support/topic/feature-request-full-php7-support-clean-log/