Matter RCP with SDK v3.0.0 on nrf54l-dk using Docker openthread/otbr image?

I have built and flashed the openthread/coprocessor sample using VS Code specifying "nrf54l15dk/nrf54l15/cpuapp".

I then tried to run it (on Ubuntu 24.04.2 LTS, x86_64) using:

sudo docker run -it --rm --privileged --name otbr --network otbr -p 8080:80 \
--sysctl "net.ipv6.conf.all.disable_ipv6=0 net.ipv4.conf.all.forwarding=1 net.ipv6.conf.all.forwarding=1" \
--volume /dev/ttyACM0:/dev/radio openthread/otbr --radio-url spinel+hdlc+uart:///dev/radio?uart-baudrate=1000000

However, it doesn't appear to be working. When I click on "Join" in the web interface it reports:

Information
There is no available Thread network currently, please wait a moment and retry it.

Would this be expected to work?

A similar attempt with "nrf52840dongle/nrf52840" was able to see two entries under Available Thread Networks.

I'm new to Matter/Thread so I apologise if I'm asking a rather clumsy question ...

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