Ref. Bluetooth
How do you enter the pass key into the iPad

Normally, the pass key is transmitted by the Bluetooth device and you enter it into the iPad via the iPad's keyboard. From the iPad help manual:

Pairing Bluetooth devices

You must first pair a Bluetooth device (such as a keyboard or headphones) with iPad before you can use it.

Pair a Bluetooth device with iPad:
1 Follow the instructions that came with the device to make it discoverable.
2 In Settings, choose General > Bluetooth, and turn Bluetooth on.
3 Select the device and, if prompted, enter the passkey or PIN number [the keyboard will pop up on the iPad]. See the instructions about the passkey or PIN that came with the device.

Note: Before you pair an Apple Wireless Keyboard, press the power button to turn the keyboard on. You can pair only one Apple Wireless Keyboard with iPad at a time. To pair a different keyboard, you must first unpair the current one.

After you pair the keyboard with iPad, the product name and a Bluetooth icon appear on the screen.

Hope this helps.

Marilyn