Please try this first on your iPhone, follow these steps>
Tap Settings.Tap General.Scroll down t.o the bottom of the page and tap Reset>Tap Reset Network Settings.
You will get a prompt warning you that this option will delete all network settings and return them to factory default settings. Tap Reset to continue.Wait while your iPhone resets its network settings.
Once the reset process is done, your network settings will return to its factory default settings. Your iPhone will also automatically restart. Then try reconnecting your iPhone to the network again.
Then try the download again.
Let me know if this does not work and we can try another solution.
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Thank you very much!