Sending a new notification based on another will create and send a new notification object while preserving the parameters of the previously created one. There is no difference between these approaches - you can choose whichever fits your scenario and each one should work. I assume that probably the device was not registered at the backend project when the first notification was sent.
Can you please elaborate a little bit more on the issue - can you currently send notifications from the portal and receive them on iOS devices seamlessly? If the problem persists we would appreciate if you could provide a sample project and information about how to reproduce the issue locally.
I am looking forward to your reply.