curl -X POST "http://localhost:5001/channel/messagesync" \
  -H "Content-Type: application/json" \
  -d '{
    "login_uid": "user123",
    "channel_id": "group123",
    "channel_type": 2,
    "start_message_seq": 1000,
    "end_message_seq": 1100,
    "limit": 50,
    "pull_mode": 0
  }'

[
  {
    "message_id": 123456789,
    "message_seq": 1001,
    "client_msg_no": "client_msg_123",
    "from_uid": "user123",
    "channel_id": "group123",
    "channel_type": 2,
    "timestamp": 1640995200,
    "payload": "SGVsbG8gV29ybGQ="
  },
  {
    "message_id": 123456790,
    "message_seq": 1002,
    "client_msg_no": "client_msg_124",
    "from_uid": "user456",
    "channel_id": "group123",
    "channel_type": 2,
    "timestamp": 1640995260,
    "payload": "SGkgdGhlcmU="
  }
]