Hello @ferranmc,
I apologize the for the delay on this topic, it has been hard to get the calling feature to work on my setup.
However, one of our domain experts got a setup to work, which includes the use of the webrtc echo cancellation configuration, which I included in the following response: Pulseaudio and module-echo-cancel YOCTO recipe - #15 by bruno.tx
Therefore, the use of alsaloop does not seem to be the way to go here.
There was no specific configuration on the /etc/bluetooth/main.conf file to get this to work.
Best Regards,
Bruno