One purchase covers both platforms, whichever store you bought from. Drag Off My Phone from your Applications folder onto this page. Apple signs every App Store receipt, so we can confirm your purchase without an account. Then a $0 checkout emails you the Windows key.
Drag the Off My Phone app here
or click to pick the receipt file. Nothing is uploaded except the receipt Apple already gave you.
Prefer a human? Send us the receipt through the support page.
The receipt lives inside the app: in Finder, right-click Off My Phone → Show Package Contents → Contents/_MASReceipt/receipt.