Try rebooting your router/network.

I used Trueplay this morning to retune my HT system without issue. I also have an iPhone 16 Pro.

Have done this and did not fix the issue. 
 

seems like it’s an issue others have had with my same speaker combo per this link 

That was last year! Have you applied the update that was released this week?

Yes I have 

I did a quick trueplay after the update on 15/4 and in addition to the update itself causing challenges with one Era 300, trueplay also failed a few times.

Trueplay started fine but I could hear it didn't sound normal and one Era 300 didn't make any sound. After restarting my 2XEra 300 and Sub4 (5min without power) everything worked again and I was able to do a trueplay without errors.

I had similar issue, Arc Ultra + 2 Era300.

Using True Play  on iPad always failed, then switch to mobile phone Android app, it works fine.

Interestingly, True Play on Sono App unable to detect the Era300 mic switch  was off, though the mic is on it's still failed,  but in Android it able to detect and give notification to turn it on.

So my suggestion is to try True Play on Android, if you have one.

I use Android and this issue happens to me incredibly often.

Also have issue with L Era 300 mic suddenly saying not “On” but it is, or the button press will not turn mic on if is “Off”.

Unplug everything, then plug in, remove Era 300s, then pair back up. It is throw of dice to get Truplay to work, then another throw of dice to see if can find a fix that day.

Very frustrating. Just want things to work, when go to use them. Tired of the song and dance of workarounds and luck.

Probably something wrong with one of your Era300, contact their support for analysis.

I'm using Google Pixel 6, in case this might be a factor.

The last option to try is to lean a bit the mobile/tablet (either Android or IOS)  device toward the speakers, rather than 90 degree, i used this trick when true play throwing error that the room is too noisy.

Not sure why an Android device could be used in any way for TruePlay?

Well, things change.

Here is the proof of the setting from my google pixel 6 Sonos App.

That is suggesting (to the best of my knowledge) , TruePlay from the microphone in the speaker. I do wish that Sonos had used different names, but as far as I’m aware, Sonos hasn’t yet overcome the fact that Android devices use a multitude of different mics.

Try it, prove me wrong if you end up waving your Android device around, I’ll honestly be delighted. 

I know how O/S works.

Applications on Windows, Mac,  Linux, IOS or Android O/S don't need to  aware what hardware used,  they send instruction to O/S, the O/S figure out what needed to translate the instruction to the Hardware through Drivers.

The hardware manufacture has responsibility to provide the drivers to ensure the O/S works with their device.

Of course all hardware not designed with the same feature, but mic is mic, nothing fancy about mic, if the feature is not valid, the O/S will simply tell the App that this instruction is not available, and the App will disable that feature.

I beg your pardon. Clearly, you know a great more than I do. 

Thanks for the education.