Hello Juan José,
you can try something like this:
2 Likes
Fortunately that works fine for me, I just encounter a small problem when trying to replace the text string with the variable that contains the JSON in the extension, I get an error:
Bad arguments to Text
The operation Text cannot accept the arguments:,[nothing]
Can you share your relevant blocks?
And the variable "json" is not empty?
No, when displaying it in a label it says the message in this format:{"packageName":"com.discord","title":"Wing","text":"ljhn"}
Try it without the block "DecodificarTextoJson"
That way it shows me "not found" on both labels
I found an example like yours...but for a list of notifications so that they obtain a list of titles, a list of texts and a list of packages...maybe it will be useful to you:
DecodificarTextToJson does nor create a dictionary , the correct method would be JsonTextDecodeWithDictionaries, see also Connectivity
However the event Notification Received will be triggered only if your app is up and running... is this what you want to do?
See also trhe documentation of the extension here App Inventor Extensions: Notification Listener | Pura Vida Apps as well as the Q&A there
Taifun
I just tried to do what was in that example but my result is the same that your other brute force example. Maybe it's better to try to make the error not appear, because the text I need is displayed fine but the error still appears.
If you are trying something, then it would really help very much to show us your relevant blocks
Taifun
If you are asking for help, I recommend you to make it as easy for others to be able to help you ...
You probably will get more feedback then...
which means in your case post a screenshot of your relevant blocks...
To download the aia file, upload it to App Inventor, open it, do some bug hunting for you, etc... this takes time, and most people will not do that...
Thank you.
Taifun
Trying to push the limits! Snippets, Tutorials and Extensions from Pura Vida Apps by 
Taifun.
Read my previous answer
Taifun