Intentional full discharge of your iPad battery is both unnecessary and inadvisable - as, with total discharge, you risk the battery entering a state of deep-discharge, this being a condition from which the battery may never recover.
If the iPad's battery is fully discharged, it may be unable to boot to a running state. Connect you iPad to suitable Power Adapter - and allow the iPad to charge, undisturbed, for at least 24 hours.
These support pages should help with troubleshooting battery and charging issues:
Charge and monitor the iPad battery - Apple Support
If your iPad won't charge – Apple Support
Verify that the charging cable is properly connected to both the iPad and Power Adapter. If the charging cable won’t properly seat or easily fit into the charging port of the iPad, this might indicate that either dirt or lint is obstructing the plug, or the plug or charging socket have been damaged. A damaged charging cable must be replaced - whereas a damaged charging port must be repaired.
If the problem is due to a visible obstruction, you may be able to remove it yourself*. With good light, using a sharpened wooden matchstick or plastic toothpick, very gently try to dislodge a visible the obstruction from the socket. Be careful to avoid damaging the delicate electrical contacts within the socket. Note that a USB-C socket has an obvious "tongue" within the socket.
(*) Removal of an obstruction is often best entrusted to the technicians at the Genius Bar of your local Apple Store or Apple Authorised Service Provider (AASP) - where the appropriate tools and expertise are available:
Genius Bar Reservation and Apple Support Options - Apple
If the charging problem is not mechanical, these support pages should help with troubleshooting battery and charging issues:
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. Most models of iPad require a Power Adapter rated at 12W (i.e., 2.4A @5V) or greater to reliably charge. 5W Power Adapters (1.0A @5V) are inadequate to charge an iPad; if the iPad charges at all, charging will be very slow. Many recent models of iPad are supplied with an Apple 20W USB-C Power Adapter.
Some third-party USB-C power adapters (and portable PowerBanks) may not support USB PD (Power Delivery). Power Delivery mutually negotiates the charging voltage; the source, load and cable are all elements involved in the negotiation protocol. Unless the Power Adapter explicitly supports USB PD, it will almost certainly fail to charge the iPad; proprietary charging standards, such as QC (Quick Charge), are not supported.
Many computer USB ports also cannot source sufficient power to charge an iPad. Unless explicitly designed for charging connected devices, computer USB ports are typically limited to 0.5-1A @5V (i.e., 2.5-5.0W).
If you continue to experience difficulties when using an appropriate Power Adapter of 12W or greater, you might be best advised to seek assistance directly from Apple Support. You can contact the Support Team using the Support link at top-right or bottom-left of this page. Alternatively you can initiate and manage your support cases from Apple devices using the excellent Apple Support App. If not already installed, the App can be downloaded from the App Store:
https://apps.apple.com/app/apple-support/id1130498044
You might also visit the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where the Apple technicians will be able to hands-on test and assess your iPad, Power Adapter and cable(s):
Genius Bar Reservation and Apple Support Options - Apple
