Custom variables are sent through url but not saved in database

I’m using custom variables like this

                        // Index, the number from 1 to 5 where this custom variable name is stored
                        // Name, the name of the variable, for example: Gender, VisitorType
                        // Value, for example: "Male", "Female" or "new", "engaged", "customer"
                        // Scope of the custom variable, "visit" means the custom variable applies to the current visit

and I see them sent in url through cvar variable, but in database nothing is saved
it’s working locally tho (in another container) but on prod it’s not working
any idea about this?

I add this to config.ini.php

Plugins[] = "CustomVariables"

and now it’s working.