Why my USB-C on my magic keyboard does not work?

The USB-C port within the spine of the Magic Keyboard for iPad can only be used to connect a Power Adapter. This port serves no other purpose; it does not support connection of any other USB devices.

If you wish to connect external storage, or other supported USB devices to your iPad, you must connect them via your iPad’s USB-C port. Multiple devices can be simultaneously connected using a suitable USB-C hub.

The USB-C port of the Magic Keyboard is for power input (charging the iPad through the keyboard). It does not claim to supply power to other devices.