Anker keyboard unpaired itself and will not reconnect

I have an Anker 7726 Bluetooth keyboard which I paired with my iPad Mini2 four months ago and have been using every day. Yesterday, the keyboard ceased to work. The batteries are good. The keyboard is not paired with any other device.

I unpaired it from the iPad, restarted both the iPad and the keyboard, turned on Bluetooth on the iPad, and asked it to pair with the keyboard. It can detect the keyboard, and attempts to pair, but the circle of spinning dots continues to spin, and a message is generated saying that pairing with the keyboard was unsuccessful.

I have followed Anker's suggestions for pairing, and Apple Support's suggestions for pairing. The keyboard still will not pair. I emphasize that it was previously paired with this iPad and was working perfectly.

Advice would be welcome.