iPad turns on when plugged in but wont charge

Hello Jayden. When troubleshooting charging issues, I would do the following (in order):

• Always try another Lightning cable and charger, preferably Apple original or MFi certified units.
• The Lightning cable 8-pin connector should be sitting flush with the housing and completely inserted. If it is not, there could be lint/dust/debris inside the port impeding a proper connection. You can clean it out with a toothpick, fine point tweezers or a dental pick. Just be careful not to damage the pins inside the Lightning Port.
• Change the battery. The battery is the weakest link and certainly for charger related issues. It is also the easiest thing to replace. Use a battery utility, such as coconutBattery (for Mac) or 3uTools (for Windows) to test the battery prior to removal. Anything less than 70% of design capacity will require replacement.
• If the battery is in good condition, you can use a USB Ammeter to determine if the device is really drawing current when it says it's charging. If it isn't drawing current, then I would change the Lightning/Charge Port. The iPad Air has a well documented history of charging problems. Over time, it loosens within the housing and this causes the flex, at the point where it connects with the port, to crack. This repair requires some micro-soldering.