This is not an error, the newer firmwares don’t have a web ui at all, they only have httpapi support.
Why did you have to upgrade? Now we can’t test proper functionality with older firmware… 
Any idea how to use the httpapi support?
I hope I can make it work again.
Apart from the broken web interface, are the speaker functions still working?
You could trick to upgrade another fimware using the standard API, as long as you can set up a local web server in your network to mimic the web structure of the public server, and use a DNS override in your router to forward traffic to your server instead of the public one. As far as I could see it doesn’t use https to download the firmware so with this typical mitm attack you can hack it bak.
Managed to fix it! 
I had to unsolder the memory from the broken one, solder it to good one, flash good one from web ui, unsolder and resolder in good place.
It was a though one!
The speaker was functioning, but the playback was not good, like old radios, hassling.
Will test tonight when arrive home.
Thank you for supporting me!
Wow. Nice.
Changed integration url to:
There’s a new "testing " branch, I’m working on bigger changes there for the new multiroom implementation. If you want to play with it, you need to replace all the files in the directory, as not only media_player.py is affected.
Switched to testing branch.
Browser = OK.
Nothing changed in HA.
Nothing changed in app.
Browser = OK.
Nothing changed in HA.
Nothing changed in app.
OK but did the speaker itself go multiroom?
Try also with eth192.168.0.151:wifi192.168.0.151 or eth0.0.0.0:wifi192.168.0.151.
No.
Will test the new commands when arrive home.
make sure your IP addresses are correct.
Checked the IP addresses. Are OK.
Ran the command for both speakers. When paused nothing happend. When both playing, the one that connects to master, it pauses and that`s it. Nothing more.
Still nothing.
Still nothing
linkplay.join
master: "media_player.Bucatarie"
entity_id: "media_player.Baie"
The above: Baie - Sound from Bucatarie, but the speaker does not play.
No multiroom on app.
linkplay.unjoin
entity_id: "media_player.Baie"
Works OK.
OK so if you join them using the app, you can unjoin them using HA’s latest method.
Interesting, seems that your older firmware supports multiroom only in wifi-direct mode only.
I’ll put back this as an option in the config file, so that users having older firmwares could still use multiroom.
IMHO multiroom in wifi-direct mode has the disadvantage that it can have weak coverage (it relies on the coverage that the master player can have in Access Point mode). In the so-called router mode players connect to each other through the building’s existing WiFi network, which can be much better, as both master and slaves are clients to access points having presumably better location and coverage.
In my case, I have a network with switches and 3 access points, one unit connects through cable, other two connect to 2 distant, separate access points. In WiFi direct mode they can’t even see each other because of walls and levels, in ‘router’ mode they connect perfectly relying on the already present network infrastructure.
When paused nothing happend. When both playing, the one that connects to master, it pauses and that`s it.
Why are you involving pause functionality in multiroom tests??
No.
The tests were made only from HA.
What I meant for “Works OK” is that it “tryes” to connect and Baie shows “Sound from Bucatarie” and no playback.
Unjoin revert it back to it`s normal state. That is what I meant.
If joining from app, unjoin from HA does nothing.
When made the first test, both speakers were on pause.
I think we should have some rules involving tests…like first test from app, second test from HA, third test combined…
You name it and I will try to do my best.
Try joining from the app, and run from browser on the master’s IP:
command=multiroom:Ungroup
You cannot run this command directly on the slave because it’s not connected to the local network, it’s connected to the master’s AP when in wifi direct mode (and that’s how the app does it by default).
Don’t play with any other functionality like pause during tests. Just keep music playing on the master during joins and unjoins.
Working as expected. Disconnects slave from master.
That’s great. At least disconnection can be done in the new way.
In case it helps, the instructions on the bottom of the page, connect and remove, were working from HA
https://github.com/nicjo814/home-assistant.io/blob/4e8adcfa627f4e0fafd754304a5c6dfb0559b1f3/source/_components/media_player.linkplay.markdown
I know. Those were using old type wifidirect multirooming.