SIP error code 422 is seen in logging for a call failure.
Explanation of Behaviour
This error relates directly to the MIN-SE and Session-Expires settings in the INVITE header.
These are interval settings used in SIP sessions - the error message 422 Session Interval Too Small indicates that the current set values do not allow enough time for the service or services to exchange requests such as INVITES.
The Min-SE setting can be left at the default of 90 in most cases.
The Session-Expires setting needs to be at least 1800 to allow for the exchange of INVITES and Re-INVITES.