I refer to page admin/ecsettings/ec_charge/add

While creating a new additional charge, a small window opens while clicking on "Add filter" or "Add calculation" buttons. But when I try to put some data in the available fields and click on Submit or Publish button (on the right), no data are inserted in the admin/ecsettings/ec_charge/add page.

There is then Fatal error: Call to undefined function ec_get_schema() in /var/www/vhosts/mywebsite.com/httpdocs/sites/all/modules/ecommerce/ec_charge/ec_charge.module on line 149