I have the Birthday Burger & Fries deal in my app. Because this voucher is normally only redeemable through online ordering, any stores where the mobile Ordering system isn't working, they are required to put the deal through manually.
Which has no connection to your app.
So it doesn't use up or expire the voucher.
So you can have the voucher in your app, show the counter crew, they put it through as a Birthday Burger & Fries Deal, and you can do this over and over, at any BK where you can't use the mobile ordering. And you can choose which burger you want, but the default is Whopper, and it's what you'll get unless you ask for something different.
I only made this realisation yesterday, but I've had the voucher in my app all month.
I don't know if the voucher expires out of your app once your birthday month is over. The T's & C's don't mention an expiry date at all. I'll report back on Tuesday, unless someone else can confirm this.
Go forth and hungus out on BK to your tummy's content. Dependant on your morals & ethics, of course ;)
Actually… just looked at the email I got for the voucher, and it says it expires after 60 days. So you have your Birthday month, and the month after, to use it.