Connect Return code values
| Value | Return Code Response | Description |
| 0 | 0x00 Connection Accepted | Connection accepted |
| 1 | 0x01 Connection Refused, unacceptable protocol version | The Server does not support the level of the MQTT protocol requested by the Client |
| 2 | 0x02 Connection Refused, identifier rejected | The Client identifier is correct UTF-8 but not allowed by the Server |
| 3 | 0x03 Connection Refused, Server unavailable | The Network Connection has been made but the MQTT service is unavailable |
| 4 | 0x04 Connection Refused, bad user name or password | The data in the user name or password is malformed |
| 5 | 0x05 Connection Refused, not authorized | The Client is not authorized to connect |
| 6-255 | Reserved for future use |
