Hello I need to monitor my cisco pdp count. Already I am using cacti

Now I have planned to use Zabbix

I dont know how to add the custom oid value for

IP-FORWARD-MIB::ipCidrRouteNumber.0

I have added like

Discovery -> Create New 
Key: ipCidrRouteNumber
SNMP OID: discovery[{#IPCIDRROUTENUMBER},1.3.6.1.4.1.9.10.48.1.2.1.2.0]

But it asking to update the Macro for the SNMP

So please help me