DHCP Option 43 is a Vendor Specific option - it is not standardized. This allows vendors to define their own sub-options and how a device should interpret them.
Below are various vendors/platforms and how each utilized Option 43.
Ubiquiti uses 43 in UniFi to inform managed devices (gateway, switches, access points, etc) of the IP address of the Network Controller. This is especially useful when these devices do not reside on the same IP network as the controller and must route to reach it.
UniFi devices expect specific hexadecimal formatting of the supplied data. To provide three parameters - Type, Length, and IP Address.
Use a Hexadecimal conversion tool to convert your IP address to hex.
For example, 172.16.0.2 in hexadecimal is AC100002.
The final value would be 0104AC100002.