Adding leads via REST API with additional fields

I'm attempting to add leads via the REST API, currently via postman, with a view to integrating with a form on our site.

The problem I'm having is that the only fields mentioned in the documentation are first_name and last_name, whereas we have more fields, e.g. email, mobile, etc. which do not seem to pull through since I'm unaware of the field names to use for these fields. The only one I managed to get to pull through was title.

Is it possible to get these other fields to pull through via the /Leads/Register endpoint, and if so could I get the field names?