Found a possible solution from Android Central questions give it a shot.

They say do the following

When pairing the keyboard with your device, it will prompt you to enter a pin and say "try 0000 or 1234." You need to:

Step 1) enter "0000" on your android device (tablet or phone keyboard)
Step 2) hit "okay"
Step 3) type "0000" and hit enter on your BLUETOOTH keyboard

Found a possible solution from Android Central questions give it a shot.

Specifically, this post says to do the following:

When pairing the keyboard with your device, it will prompt you to enter a pin and say "try 0000 or 1234." You need to:

Step 1) enter "0000" on your android device (tablet or phone keyboard)
Step 2) hit "okay"
Step 3) type "0000" and hit enter on your BLUETOOTH keyboard