Does anyone help me to understand how set-up config file to work with extra accounting?

I need to let it write into db the body part of the INVITE message but I’m not sure to understand at all the docs…

modparam("acc", "db_url", "mysql://user:password@localhost/openser")

modparam(”acc”, ”db_extra”, ”ct=$rb”)

I think I miss something, cause it doesn’t work…!!!

Please help me!!!

Davide