Connect your iPad to its Power Adapter - and allow it to charge for at least an hour. Then, whilst still connected to the Power Adapter:
- On an iPad with a Home button: Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.
- On an iPad with Face ID: Press and quickly release the volume up button, press and quickly release the volume down button, then press and hold the top button. When the Apple logo appears, release the button.
If still having difficulties with charging your iPad, this support page might be helpful:
https://support.apple.com/en-us/HT201569
So as to eliminate the possibility of a bad Power Adapter or connecting cable, it may be necessary to systematically change both for “known good” examples of each. If still experiencing issues thereafter, it may be necessary to seek assistance directly from Apple Support or your local Apple Store - who can examine and test your iPad, charger and cable.
If you choose to contact Apple Support, you will find the Contact Support link at top-right of this page.
I hope this information and guidance proves to be helpful in resolving the issue.