This article covers How to configure SNMP Trap v3 on the Nagios XI server.
The main difference between v2 and v3 traps is the authentication mechanisms. v2 is much simpler by design whereas v3 has multiple layers of authentication to strengthen it. Probably the biggest difference is that the SNMP Trap Daemon (snmptrapd) is configured by default to accept v2 traps from any device regardless of what SNMP community is provided.
However snmptrapd cannot be configured to accept traps v3 from any device, it must be configured before it can receive an SNMP v3 trap.
The default SNMP Trap configuration is stored in the /etc/snmp/snmptrapd.conf file and contains just two lines:
traphandle default /usr/sbin/snmptthandler
The disableAuthorization directive allows SNMP v2 traps from any device to be sent to Nagios XI.
Even if this line exists the Nagios XI server will not be able to receive SNMP v3 traps unless the server has been specifically configured for SNMP v3 traps.