What do you want to happen after receiving a message?
Taifun
For the moment change the textbox with either "Received" or the value number "1234567"
Try to set ReceivingEnabled to Always in event Screen1.Initialize
Which Android device and Android version are you using for your tests?
Did you test this after building the app using the apk file?
Taifun
Changed it to this. Still di not do it. It is built (APK) not using the companion. Samsung A53 Android 12
The attached example project works fine for me on Samsung Galaxy A54 running Android 16
Build the app and test it using the apk file.
it asks automatically for post notification and receive sms permission while starting the app.
Keep the app open and use another device to send a sms to your phone number.
receiving.aia (1.9 KB)
Taifun
tried a different phone - nope
tried yours - no
does it only work in certain countries?
Did you receive the sms in your default sms app?
Probably it has been received as rcs message? In this case your app will not be able to receive it... see here how to adjust it
I have seen you updated the subject and added "using itoo". You do not need itoo to receive a sms. And as the texting component is restricted in the background to only send a notification after a sms has been received, you will need a specialized extension which is able to receive the sms in the background in case you want to trigger something..
I would not have spent time to create the extension otherwise App Inventor Extensions: SMS Receiver | Pura Vida Apps
Taifun
Yep, that was it . Turned RCS off and it works fine. Thats gonna be a bit off a problem 
Is this of any use to anyone?
That is something new that was not available a few years ago when I was researching RCS Messaging.
It seems we have to hit Google's HTTP endpoints to send/manage messages via RCS... Which should rather have been part of the native Android SDK...