This warning occurred because the printer is using a different paper size than the one you selected.
Sounds like a bug? An update is available!
If this error message is unexpected, please install the latest Print to Size update (version 1.9). It includes a fix for a bug that causes this message to wrongly appear on iOS 16. To get the app update, open the Print to Size page on the App Store (or just click here) and tap on the Update button.
Why did I get a blank print?
If the app had tried to print anyway, then your print could have been wrong, wasting your ink and paper. Instead you can reuse your blank sheet of paper and try again.
What can I do to fix this issue?
Choose a different paper size. If you tap on “Choose a Supported Paper Size”, the app will show you the paper sizes that are currently available in your printer.
If you have another way to print at the desired size (such as your printer manufacturer’s own app or a computer), you can export the page and print it outside the app, as explained here.
If the app is wrong and your paper size is supported, please check that you are using the latest Print to Size update (version 1.9).
It could also be a problem in your printer’s paper detection system. Please try turning off your printer and your iPhone or iPad, then turning them back on. It may help to open and close your paper trays or to refill them, in case your printer is failing to detect paper.