Availability Replica Join State
Availability Replica is not joined.
This policy checks the join state of the availability replica. The policy is in an unhealthy state when the availability replica is added to the availability group, but is not joined properly. The policy is otherwise in a healthy state.
The secondary replica is not joined to the availability group. For an availability replica to be successfully joined to the availability group, the join state must be Joined Standalone Instance (1) or Joined Failover Cluster (2).
Use Transact-SQL, PowerShell, or SQL Server Management Studio to join the secondary replica to the availability group. For more information about joining secondary replicas to availability groups, see Joining a Secondary Replica to an Availability Group (SQL Server).