IS-M-CA Collective Invoice

Dear all,

I am trying to link one account with a collective bill account using T. code CAA1, however i am getting this error message:

'Contract account category is defined for collective invoice accounts, but the collective invoices function is not active.' Message nº 3573

can anyone please tell me where in customizing i can activate the collective invoices function?

Thanks i advance for all your help.

Regards, Renato