What should the 'device_id' contain and is it a mandatory field?

The inclusion of the device_id field in the request is non-compulsory, and is not required for the device fingerprinting module. It should contain any device related information that you may receive from your own device fingerprinting or a third-party module.

In case this data is available, it is recommended to include it in the request to further enhance the information for a user.