According to the Apple Device Support Reference Materials, the three troubleshooting steps that you should try to resolve the issue of iPad not charging are:

Force restart the iPad.  This can help clear any software glitches that may prevent the iPad from recognizing the power source or charging properly 1 2 .  The steps to force restart the iPad depend on whether it has a Home button or not 1 .

Make sure that the device isn’t too hot or too cold.  Extreme temperatures can affect the battery performance and charging ability of the iPad 1 3 .  The iPad should be kept within the acceptable operating temperatures of 0° to 35° C (32° to 95° F) 3 .

Try charging with a different power adapter and cable.  The power adapter and cable may be damaged or incompatible with the iPad, causing the charging issue 1 4 .  It is recommended to use the original Apple power adapter and cable that came with the iPad, or other Apple-certified accessories 4 .

The other two options, D and E, are not relevant or helpful for resolving the charging issue.  Backing up the device and erasing all content and settings may be useful for other issues, such as storage or performance problems, but not for charging problems 5 . Enabling Optimized Battery Charging is a feature that helps extend the battery lifespan by reducing the time that the iPad spends fully charged.  It does not affect the charging speed or ability of the iPad.  References :  1 :  Fix issues with charging - Apple Support   2 :  iPad won’t charge, Try these tips to fix it - Geeky Gadgets   3 :  iPad not charging: 6 solutions - 9to5Mac   4 :  How to fix an iPad that won’t charge: 8 troubleshooting tips - Macworld   5 : Erase all content and settings from iPad - Apple Support :  About Optimized Battery Charging on your iPhone, iPad, and iPod touch - Apple Support