Bluez L2CAP CoC to Android / iOS Credit based flow failing

Question

I've been trying to get a connection from Android using createL2capChannel or createInsecureL2capChannel (and iOS) to a Raspberry Pi which has created a BTPROTO_L2CAP SOCK_SEQPACKET Bluetooth socket which it is accepting, running Bluez 5.50 but they are failing at the LE Credit Based Flow step.

Running WireShark with a nRF BLE sniffer I see it is failing at the LE Credit Based Connection Response with LE_PSM not supported:

Command: LE Credit Based Connection Response
    Command Code: LE Credit Based Connection Response (0x15)
    Command Identifier: 0x02
    Command Length: 10
    Destination CID: Null identifier (0x0000)
    MTU: 0
    MPS: 0
    Initial Credits: 0
    LE Result: Connection Refused - LE_PSM Not Supported (0x0002)

I've tried various PSMs: 0x1001, 0xf3, 0x25 without any difference. I have also seen that BlueKitche BTStack works, so I know the iOS / Android code is OK.

Does anyone know how to actually configure Bluez to correctly support LE L2Cap CoC credit based flow on the Pi?

Answer 1

Solved thanks to the Bluez Slack channel. I followed https://git.kernel.org/pub/scm/bluetooth/bluez.git/tree/tools/l2test.c#n573 to get the correct settings from do_listen().