Create Bill for Payment

Any API or feature which is in creation to create a bill after a payment give back complete = 1

Is it possible also possible to show in the future the eventid and registrationid in the registation list for a export ?

You should be able to hook up a plugin to listen on signals.event.registration_state_updated.
This signal gets a registration and the previuos state, so generating a receipt should be possible.

We’ d love to have receipt generation as part of the core, as long as it’s reasonably flexible (e.g. using an HTML template uploaded by the user)!