On the basis of your description, your iPad battery is exhibiting symptoms typical of battery failure - where the battery cannot retain adequate charge to run your iPad. The battery will likely require replacement.
You might be well advised to seek assistance directly from Apple Support - and request a remote battery diagnostic.
If you battery is defective, they will also provide appropriate advice. The Contact Support link is at top-right of this page. Alternatively, you can initiate a support case using the Apple Support App:
https://apps.apple.com/gb/app/apple-support/id1130498044
Alternatively, You might visit the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where the technicians will be able to test and assess your iPad, Power Adapter and cable(s). If your iPad requires replacement, you’ll be in the best possible place to explore your available options:
Genius Bar Reservation and Apple Support Options - Apple
As a further alternative, you can use Apple’s mail-in service:
iPad Service & Repair - Apple Support
Charge and monitor the iPad battery - Apple Support