If the second Bluetooth device is unable to establish a secure connection with your iPhone due to a software fault, turning pairing mode off and back on may be able to resolve the issue. Here's how to do it if you haven't already:

1. On your other Bluetooth device, look for the switch button (Bluetooth button). Every Bluetooth device must feature a switch that allows you to turn pairing mode on or off quickly.
2. To exit pairing mode, press and hold that switch or button for a few seconds.
3. Wait around 30 seconds before pressing the switch or button to return it to pairing mode.