My iPad Air (4th G.) won't charge.

As described, either your Power Adapter is faulty - or your battery has perhaps failed and will require replacement:

If your iPad won't charge – Apple Support

Charge and monitor the iPad battery - Apple Support

iPad Repair – Official Apple Support

We are also seeing frequent reports of issues charging iPad Air4 in high ambient temperatures. If this applies to you, try charging in a cooler location.

Assuming that the iPad remains functional, you would be well advised to directly contact Apple Support - and request a remote battery test. The result of the test may better inform your next steps.

You will find the Get Support link at top-right of this page. Alternatively, you can open a support case using the excellent Apple Support App. If not already installed on your iPad, the App can be downloaded from the App Store:

https://apps.apple.com/gb/app/apple-support/id1130498044

As a further alternative, you might visit the Genius Bar at your local Apple Store - where the technicians will be able to test and assess you iPad.

You need to search online for your nearest, “local” Apple store location and call to make an appointment to have your Apple iPad diagnosed and options presented you.

Bring both the iPad’s power/charge cable and Apple power/charging adapter block.

Failing that,

You need to contact Apple support via the contact support link located at the upper right hand corner of every Webpage of these Apple support communities.

Use the Hardware Repair & Battery usage & Charging support categories.

OR

by installing and using the Apple Support app found in the iOS App Store.

Tap the iOS App Store link below.

https://apps.apple.com/us/app/apple-support/id1130498044

OR

Call contact Apple via the support numbers found in the link bekow.

Contact - How to Contact Us - Apple

Tap the link below.

https://www.apple.com/contact/

Best of Luck to You!