How to recreate 'Register Myself'/'Register Someone Else' buttons on Events through the API

Hi,

I've asked a similar question in another discussion post:
How to recreate 'Cancel My Registration' button on Events through the API" however i'd like some insight on how to register rather than cancel.

That old post explains how most of registration is done through the cart. I've created OrderLines with the right prices and delivery data and posted to the cart. However our manually created carts are missing fields such as 'OrderLineId' and 'DeliveryId' that seem to be required to make this work.

Are these Ids generated manually as well or is there an API endpoint that generates these guids as well?

Thanks