# Mandatory Sender ID upgrade

This release intentionally removes the application Default Sender ID fallback. Every single and bulk message candidate must now include `sender_id`, and the exact value must be active and assigned to the authenticated application.

Existing nonempty valid `applications.settings_json.default_sender_id` values are migrated into tenant Sender ID inventory records and application assignments. Unrelated settings remain unchanged. The legacy key is retained for rollback evidence but is ignored by runtime code and can no longer be managed in the Developer Center.

Clients must begin sending their assigned `sender_id` before the new code is activated. Deployment order: stop SMPP runtime, back up the database, deploy code and migrations, verify backfilled assignments, clear/rebuild caches, restart runtime, and smoke test. Accepted and queued messages retain their already resolved sender values.

Rollback restores the previous code and rolls back the assignment tables. Clients updated to send `sender_id` remain compatible with the old endpoint, but assignments created only after migration must be reconciled before retrying the upgrade. No message data is rewritten or deleted.