Fullfilment workflow

I have created some manual orders on my test site. Via the API I need to update the order to fulfilled and add the tracking details etc. ( I can see how to do this in the docs)
The issue is when I set the order to paid the it automatically sets to FULLFILED. (which is incorrected as the tracking is not added)

Unless I am not understanding the workflow.

I had to add shipping then select add a shipping method. The setting to paid didn’t change the fullfilment status.