Read the response in its timer context
422 is defined for session timer negotiation when the proposed interval is below an acceptable minimum. The response carries Min-SE. Compare that value with the rejected request’s Session-Expires and record which peer generated the response.
This is different from 423, which can reject an overly short registration expiration. Read the method and header names before editing a similarly named expiry setting in the PBX interface.
Inspect the next request
A client retry must accommodate the learned minimum according to RFC 4028. Look for a new request transaction with updated timer values rather than repeated transmission of the same rejected proposal. Preserve the whole negotiation if more than one intermediary contributes a minimum.
On a PBX with separate call legs, compare the timer policy and actual requests on each side. A phone accepting an internal call does not demonstrate that the carrier accepted the interval on an outbound call.
Verify negotiation and the later refresh
Check which configuration owner controls session timer policy for the affected endpoint or trunk. Use that owner’s supported controls and verify the generated result. Do not change registration refresh, RTP inactivity and session timers together.
After the request is accepted, record the negotiated interval and refresher. Keep the call active long enough to observe a successful refresh, then test ordinary hangup. Removing the initial 422 is only the establishment check; a later refresh can still fail because of routing, transport or another policy mismatch.
Sources & applicability
Primary references for the technical details above. Operational examples and planning checklists are VoIP.info editorial guidance.
Examples require adaptation to your topology. No live PBX or hardware testing is claimed.