G'day John Earl,
Thank you for using Apple Support Communities.
I understand that you are having an issue logging in and using your iPad's Amazon app. I know how important it is to make sure that you're able to use all of your iPad's apps. I have several things for you to try.
First, it's important to make sure that you have a recent backup of your iPad's important data. Use How to back up your iPhone, iPad, and iPod touch to make sure you have a recent backup.
Next, you mention that the Amazon email and password combination is working fine on other devices. What I'd recommend, is opening the App Store on your iPad and checking for any available Amazon app updates to make sure you're using the latest app version.
If you still have the issue, use Delete music, movies, apps, and other content from your iPhone, iPad, or iPod touch to delete the Amazon app from your iPad, specifically, this section:
- Press and hold the app until it jiggles.
- Tap the in the upper-left corner to delete.
You might be asked to confirm that you want to delete the app. If you see a pop-up that says, "Deleting [app name] will also delete all of its data," tap Delete.
Once you've deleted the Amazon app, redownload from the App Store. And then Restart your iPhone, iPad, or iPod touch and try to log in again.
If you still need assistance I recommend contacting Amazon Support directly about this issue.
Best Regards.