iPad flashes and won't turn on while charging

Verify that your charging cable is undamaged and is properly connected to both your Power Adapter and the iPad.

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 (never metallic) 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 that is easily damaged.

(*) 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) intended for older models of iPhone are inadequate to charge an iPad; if the iPad charges at all, charging will be very slow. Recent models of iPad are supplied with a 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 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 technicians will be able to test and assess your iPad, Power Adapter and cable(s):

Genius Bar Reservation and Apple Support Options - Apple

Check the charger. Is the original used and is it suitable for the iPad model. The working condition of the charger can be checked by connecting it to another device. You also need to inspect the accessories for mechanical damage — if any, the equipment needs to be replaced with a new one. 1

Clean the connection connector. To do this, carefully inspect it with a flashlight and clean it using a needle, toothpick or toothbrush. It is important to act carefully so as not to damage the connector components. 13

Wait if the battery is completely drained. In this case, you need to wait at least half an hour for the device to charge up a little — most often the indicator goes off within 5-10 minutes. 1

Perform a "hard" reboot. To do this, hold down the Home and Power buttons on the iPad at the same time and hold them down until the Apple logo appears on the tablet screen (10-15 seconds). 3

Contact the service center. If none of the methods helped, the specialists will carry out a comprehensive diagnosis, repair or replacement of components.

Shaky-shiner9 wrote:

To do this, carefully inspect it with a flashlight and clean it using a needle, toothpick or toothbrush. It is important to act carefully so as not to damage the connector components.

Bad advice. You should never insert any metallic object into the charging connector that is not the mating plug. Metal objects, such as a needle, can create a short-circuit and cause irreparable damage.