curl --request PATCH \
  --url https://your-instance.example.com/api/contacts/{id}/block \
  --header 'Authorization: Bearer <token>'

{
  "message": "Contact blocked successfully",
  "data": {
    "contact": {
      "_id": "64f0a1b2c3d4e5f6a7b8c9d0",
      "firstName": "Jane",
      "lastName": "Doe"
    },
    "syncedDeviceIds": [
      "device-abc123"
    ],
    "removedDeviceIds": []
  }
}