I recently have been unable to connect my iPad with Word for iOS. Word has been able to connect to box and OneDrive without any issues.
At this point, I go to Word, try to "add a place" under the "Open" menu. I try to "connect to a cloud service", and tap Dropbox. It opens the Dropbox app with a window asking me to allow access to Dropbox. I click Allow. An "Authorizing" bubble pops up for about 1/2 second, and then closes. It takes me back to Word, and Dropbox is not added as a source to open from.
It also does not work to go through the backdoor, of trying to "Open" from Other Locations > More, and then finding the Dropbox folder in "Browse." I click on the file to open and it simply opens again to the startup "Open" screen and doesn't open anything.
I also have the exact problem that @ATurk86 and @Mrop59 are having while setting up a new iPad 7th generation. Integration on my much older iPad Pro 9.7 (2016) works flawlessly. Will read the article that @Jay has posted and report back. If anyone has further suggestions or information, please let me know. Note that I haven't (yet anyway) searched the Microsoft forums for a possible solution.
Edit: didn't find anything in the article that specifically addresses the problem described in the OP
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