This issue can sometimes happen when the QR code is generated using mobile data, rather than Wi-Fi. Try connecting to a stable Wi-Fi network and generating the QR code again. You can also try restarting the app, and then selecting the QR code right at the post office.

If this doesn't work, there's also an option to download the label as a PDF, which can be emailed or digitally sent to most post offices, and they can print out the label from there.

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