Try other known good, compatible power/charging cables and/or other known good 12, 18 or 20W power/charging adapter blocks to test for current cable and/or power/charging block failures.
Power/charge cables and/or power/charge adapter blocks can AND DO fail at any time for any reason.
If no spare power/charging cables or power/charging adapter blocks or NO joy on getting this iPad charging, you can purchase new cables and power/charging blocks from your nearest, “local” Apple Store location or from Apple's own Website.
OR
Purchase new, third party Apple MFi ( Made for iOS devices ) certified power/charging cable and adapter block, from online retail, mobile device sellers, to test with, in order to determine that your existing power/charging cables and adapter block is bad/faulty.
OR, if no success with brand new power/charging cables and/or power/charging adapter blocks,
You may need to use the “Get Support” link, at the top far upper right hand corner of every Apple Support Community Webpage, and make an appointment for your nearest, local Apple Store and bring your iPad and charging cable and adapter block, to the appointment, for Apple employees to test/diagnose and options presented to you.
Best of Luck to You!