Thank you for your answer. I know this part of the guideline unfortunately. Is there a solution to achieve what I want to do ?

I managed to capture the sysdiagnose file ("Trigger a sysdiagnose on the device by simultaneously pressing and releasing both side volume buttons and side button" not easy to do btw .. ) I don't know what to look for, this log is really long. Yes I am just storing 1 value with an iP address. I did a new test, now I can from the appleTV update this value and got it on my iPhone, but not the opposite way . Do you know what can cause this ? The source code is the same. I will try from another iPhone maybe ...