I plugged in my 10 foot charger into my iPad 2017 model and it says accessory is no longer supported, even though I have been using that same charger every single day for 3 months. I also plug it in to my iPhone and guess what, it works! This doesn’t make any sense!
iPad Wi-Fi, iOS 11.3
That can happen (even with an OEM Apple cable) if it's been "compromised". I've seen it before in an Apple OEM Lightning cable where it had been excessively flexed at the connector.
Apple doesn't sell one that long, so I'm guessing it's aftermarket? If it's MFi certified then you should see if there's a warranty from the manufacturer. They all have different terms. In my experience Apple will only provide a warranty replacement if the jacket shows no signs of external damage.
If it's not MFi then I've seen quite a few that reported "Accessory Not Supported". Sometimes that only happens after an iOS update. I've even had one knock out my MacBook Pro, although I was able to get it working again by disconnecting the battery.
This accessory may not be compatible
