My iPad Pro is charging very slowly what could it be

If you already tried (to no avail) ALL the steps provided in this support article:--> If your iPad won't charge - Apple Support, I suggest that you contact Apple Support directly, using this link:--> Get Support , or make an appointment and have your device (along with your charger+cable) inspected at an Apple Store or AASP (Apple Authorized Service Provider) among this list:--> Apple – Location Selector

After checking it out, they'll give you all the available options.

Regards

Giulio

Are you describing a change in established behaviour? Has the Power Adapter been used before - and charging previously been as expected?

Be aware that most models of iPad require a Power Adapter rated at a minimum of 10-12W to reliably charge. Many iPhone Power Adapters are rated at only 5W, this being inadequate to charge an iPad. If using a 5W Power Adapter, if charging occurs at all, charging will be very slow.

Assuming that your Power Adapter is suitable from charging your iPad, these support pages should help with troubleshooting:

Charge and monitor the iPad battery - Apple Support

If your iPad won't charge – Apple Support

Troubleshooting generally requires substitution of the Power Adapter and cable for another known-good item.

If you continue to experience difficulties, you might be best advised to visit the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where the technicians will be able to test and assess your iPad, Power Adapter and cable(s):

Genius Bar Reservation and Apple Support Options - Apple