Many users have reported difficulties with the Kindle App. The issue is reportedly known to Amazon, the App Developer.
Ensure that you have updated your iPad to the most recent version supported by your iPad - and that you have also updated the Kindle App.
iPadOS 16.6.1
- iPad Pro (all models)
- iPad Air (3rd generation and later)
- iPad (5th generation and later)
- iPad mini (5th generation and later)
iPadOS 15.7.9
Older models of iPad will be limited to a much earlier version of iOS.
If difficulties persist, try deleting the Kindle App from your iPad - and then perform a forced restart before reinstalling the Kindle App:
Delete apps on your iPhone, iPad, and iPod touch - Apple Support
Force restart iPad - Apple Support
Otherwise, you'll need to seek assistance from the Kindle App Developer (Amazon).