public is normally used as a Read Only SNMP credential. Also, using public is not wise - it is the first thing someone will try if they want to hack into your systems!
If you do a 'sh run | inc snmp' on the routers, do the 'snmp-server community' lines end with 'RO' or 'RW'?
Oh, I see, it seems I figure out my problem.
I type this on CLI of the routers
snmp-server community public RW
I think I have to change public to any secure credential
Thank you very much, I really appreciate your help.
As long as the <string> from the 'snmp-server community <string> RW' command matches the <string> you specify in NTA (and it is an RW line) it should work; even if you have used 'public'.
The advice to not use public/private is just best practice since they are a universal default that offers about as much protection as a chocolate tea-cosy!