I can't download (update) files in iCloud Drive on my iPhone 6 over 4G connection. It only works with WiFi. Can someone help me? Thanks.
Please see this image which shows you how to enable cellular data.
I had the same problem on my iPhone8 and got it resolved with Apple Support. Apparently, while the settings (mobile data on, iCloud enabled) may be correct, the phone may not detect them correctly. The solution is to turn mobile data off, shut down the phone. Start the phone up again and then turn mobile data back on. Shutting down the phone must be done differently for this to work. Press volume down, press volume up, then press and hold the power button until the apple logo appears.
I finally figured it out after half a year...
- MAKE SURE YOUR SETTINGS HAS CELLULAR DATA ON!
it should work by then.. if not the second step would be @robs post.
(Thank you rob for your post! it made me check the cellular data when it didn't pop up in icloud menu)
The way I solved that issue is to logoff from and login in icloud and turn plane mode on for 30s. See https://discussions.apple.com/thread/8246057.