That’s very strange, Android should never ask you for a pin code to connect to the Mooshimeter. A few things to try:
1. Resetting the Mooshimeter (open the case and press the small button on the side under the battery)
2. Rebooting the phone
3. Replacing the Mooshimeter batteries
I haven’t seen anybody else reporting this specific issue, so I’d try those operations first.
I hope it helps, let me know how it goes. Best