Originally Posted by
BubbaX
When you buy the ticket, and go to the website/app to check your booking, you will see an invitation to upgrade with miles. If you click on that, it will always lead to a page that says "give FB a phone call". When you call them, they will tell you an upgrade is not possible.
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I personally confirm this. Tried many times. On KL you can upgrade only when check-in opens. If not online you can try at the airport.