How do I make in-app purchases appear within my apps on all of my devices? I have purchased an in-app purchase for flightradar24 on my iPhone, and the in-app purchase has not appeared on my other devices. 

The app itself has synced to my other devices, however, when I purchased the add-on 'Arrivals &amp; Departure' for £1.99 it only appears on the device I purchased it from, not on my other devices. 

How can I get the 'Arrivals &amp; Departure' in-app purchase to appear on my other devices as well?
Assuming you've used the same Apple ID on all devices you shouldn't have a problem. However, you will need to restore the in-app purchase on all devices you didn't originally use to make the purchase.

To do this, you will need to navigate around the app and look for an option labelled something like restore in-app purchases (or similar). Many apps will put this option within their own settings page, but I can't advise you exactly where it will be for this app (as I don't personally use it).

If you can't find an option anywhere to restore the in-app purchase, I would go to their dedicated iOS forum page and ask for help.