Bluetooth connection dropped, wrong PIN reported by mobile device, SSP profile used

[camilzi]

Describe the problem
In case of SSP Android (Xiaomi Redmi Note 9 Pro, Android 11) mobile phone report "wrong PIN" and drop the connection.
In case of iPhone (SE 2020 with iOS 16 and 7 with iOS 15.7) everything is working well.

I don't like blame on Xiaomi because balenaSound is the only one Bluetooth Device causing such errors on Xiaomi phone. I found also in different other forums similar issues (reported even 2019, 2020 or later) but nobody were able to present solution (or I didn't find it).

To Reproduce
Steps to reproduce the behavior:

1. Configure SSP on balenaSound
2. Get Xiaomi Redmi 9 Pro with Android 11
3. Click on balenaSound Bluetooth devices and try to connect
4. See error "wrong PIN"

Expected behavior
Connection to balenaSound is possible In SSP mode.

Screenshots
If applicable, add screenshots to help explain your problem.

Device information

• Raspberry Pi 4
• Device type balenaCloud using 64bit OS
• balenaOS version: the current development version from October 2022, multiple older versions tested, no particular version affected, seems to be a generic issue.

Additional context
In case of balenaSound with Bluetooth configured in legacy mode with PIN Xiaomi phone get connected, no issues are reported. iPhone's don't work anymore because iOS is now forcing SSP.

Can you please at least share more details how to tune/modify the Bluetooth settings in balenaSound environment. Is there any official interface/cli-tool which should be used?