Your AirPods may not charge on the USB-C Magnetic Wireless Charging Cable if your AirPods case is not a wireless charging case.

AirPods (2nd generation) were sold with either the original case or the AirPods Wireless Charging Case. To check which case you have:

• LED indicator on the outside of the case: Wireless Charging Case. This case works with the USB-C Magnetic Wireless Charging Cable.
• LED indicator inside the case when you open the lid: not a wireless charging case. This case must be charged with a Lightning cable.

When your AirPods are charging, the white LED on the USB-C Magnetic Wireless Charging Cable blinks slowly.