first of all thanks ermal for the kind reply.
i've been successfully able to accomplish what i want to do.
For the sake of pfsense community, i want to share with you guys here.
Actually, what i want to do is using captive-portal with freeradius attr, Max-All-Session with sql database (freeradius server is on another box). So, that i can generate prepaid account with time limit (eg: 5 hours of usage) which the account will be automatically expired/rejected when the limit is exceeded.
It seems that my problem lies in config file of freeradius. I need to add some line for noresetcounter. In freeradius version 2.0, the setting to be enable is at ../modules/counter ;to enable noresetcounter, add a line under instantiate to enable noresetcounter in radiusd.conf, and a line to enable noresetcounterin /site-enable/default under authorize. I installed freeradius with -mysql support.