Unable to configure sync between the iOS app and Dropbox either on phone or tablet. There is no input box after the "Step 2: Enter the code provided by Dropbox. Tested on iOS 10.3.3 (full size iPad) and 11.3.1 (iPad Mini, iPhone), all have the same problem.
The textbox should be there but maybe for some reason it has no visible border. Try to tap on the area below the message and that should popup the keyboard so you’ll know you are on the input box.
Thanks Laurent, found it!