Check the debug messages when adding by access key fails, you should get a good reason why.
I'm going to assume that your server access key is out of date. It shouldn't be since it updates periodically while MC is running.
You can find out by going to the access key in media network on the server and clicking test on it.
I deleted the server from the iPhone app and tried again with 3.37.423 and connecting via access key worked
I can play ALAC untranscoded fine. So yours must be either
1) Protected or
2) Too high of a sample rate in which case you'll need to turn on transcoding. My iPhone XS will play 24 bit 48k ALAC.In the App streaming means CloudPlay or RadioParadise. I agree it's a bit confusing.
Transcode on the JRemote settings is off. Turning it on, the music plays.
That said, JRemote should be able to play ALAC files natively.
None of my ALAC files are protected. Most are 44.1/16, and that's what I tried to play.
I tried the Files app with the same files, and they play fine, so the iPhone can play the files.
M4A is not checked in "Audio Formats to Convert" as the iPhone and iPad can play all my ALAC files.
Adding M4A to the list and changing the setting to always convert audio, and I still get the same error.
Any ideas or suggestion for the Audio Conversion options? Is there another place to check for transcoding settings?