This can be very frustrating but it's usually a very simple fix.
After you have scanned the QR code or manually typed in the device number, you will need to choose a name for the device.
The name has to be capital or lower case letters and numbers. Symbols or punctuation marks (a comma, apostrophe etc) cannot be used. If you try to use them, it will say that binding has failed.
Next, you can choose your relationship to the tracker.
Then press OK. It should now bind.
If the APP still doesn't like what you have entered, please contact email@example.com with a screenshot of the issue.