# set.device.custom_data
Set or update custom data fields, such as a customer-defined serial number (CustomerSn) or informational messages (msg0-msg9).
The key must be either `CustomerSn` or `msg` followed by a number from 0 to 9. The value must consist of printable characters.
Each `msg` field value must be less than 128 bytes in length.
## Parameters
| param | Object | The container for the custom data. |
| param.key | String | The name of the custom data field to set. Valid values: `CustomerSn`, `msg0`, `msg1`, `msg2`, `msg3`, `msg4`, `msg5`, `msg6`, `msg7`, `msg8`, `msg9` |
| param.value | String | The value to assign to the custom data field. For `msg` fields, the length must be less than 128 bytes. |
## Examples
### Request
```json
{
"cmd": "set.device.custom_data",
"param": {
"key": "CustomerSn",
"value": "CUSTSN-12345"
},
"ts": 419304089,
"token": "Y0Ijoro/",
"account": "super"
}
```
### Response
```json
{
"code": 0,
"when": 3521,
"msg": "ok",
"desc": "set.device.custom_data"
}
```