curl -X POST http://localhost:5080/api/v1/alerts/incidents/$INCIDENT_ID/responders \
  -H "authorization: Bearer $MS_TOKEN" \
  -H "content-type: application/json" \
  -d '{"user_ids": ["<another-user-id>"]}'

{
  "id": "3KEDNEyqouYJeBDTLTMTBui7XHW",
  "org_id": "<organization-id>",
  "rule_id": "3KEDBLvTYO6DnWi8H9S9MNLpPT7",
  "escalation_policy_id": "<policy-id>",
  "status": "open",
  "severity": "critical",
  "summary": "High error rate · checkout",
  "fingerprint": "2b7f5329675de7077c74ffa2646a36cd3adf16f80f523270332894d1ff630632",
  "current_step": 0,
  "current_loop": 0,
  "current_step_started_at": 1790000300000000,
  "assignees": [
    "<user-id>",
    "<another-user-id>"
  ],
  "labels": {
    "service": "checkout"
  },
  "annotations": {},
  "trace_ids": [],
  "host_ids": [],
  "affected_services": [
    "checkout"
  ],
  "created_at": 1790000000000000,
  "acknowledged_at": null,
  "acknowledged_by": null,
  "resolved_at": null,
  "resolved_by": null,
  "team_id": "<team-id>",
  "routing": {
    "reason": "default"
  },
  "snoozed_until": null,
  "snoozed_by": null,
  "assignees_pinned": false,
  "severity_set_by": null,
  "merged_into": null,
  "dispatch_round": 1,
  "dispatch_reason": "responder_added",
  "revision": 4
}