This counter tracks the number of ADD PARTY REJECT messages, sent when a request to add a party to a multipoint SVC is refused that this port has received, per the description. This is the failure-mode counterpart to add-party acknowledgements, so a rising trend here on a port that hosts conferencing traffic points to a specific problem adding new legs -- commonly resource exhaustion on the target leg or an incompatible traffic descriptor -- rather than a general call-failure issue. For example, if this counter rises in lockstep with NumAddPtyPduTx, essentially every add-party attempt on this port is being refused, which would justify checking the target party's QoS/traffic descriptor compatibility.