Cannot join group unless leader / co-ordinator is known

[gjhw]

I have a flow configured so that I can ask Alexa to join a zone to another that is already playing, however, this will generate the following error if the zone isn't the group leader / co-ordinator:

Error: HTTP response code 500 for "urn:schemas-upnp-org:service:AVTransport:1#SetAVTransportURI"

It's not really possible to keep track of the leader, especially if I use another flow to leave the group as the leader then passes to another unpredictable zone.

[gjhw]

Following up on this some more, it appears that when a zone is part of a group, the URI is always:
x-rincon:RINCON_[MAC]01400 (where [MAC] is the MAC address of the group leader.

So for now I can parse the URI to establish the group leader but maybe it is possible to have the node deal with it a bit better without excess code?

Once I have figured out my JSON to establish a group leader I will share it here in case it helps.