In some cases the easiest solution to a problem is to just start over. Do so on iOS with these steps:
Un-pair the pin.
Turn the pin on and then hold the button on the pin for 5s (until the pin displays a message saying "Pairing: add the pin in your app").
Remove the pin in the app.
Go to the "MY PINS" tab in the app. Then press the pin for a couple of seconds until the app asks you if you're sure you want to delete the pin and click yes. If the list is empty no action is needed.
Manually remove the pin from the phone.
Go to your bluetooth settings (settings > bluetooth, may be different on some devices). Select the pin in the list "My devices" (if it appears there) and click "Forget this device".
Turn Bluetooth on and off.
To make sure the Bluetooths cache is empty turn your bluetooth radio off and then on again. (To can do this in the same place as in step 3).
Good work! Now the pin and the phone are unpaired from each other. Restart the app and try connecting again.