Broadcast string message on esp8266 with painlessmesh

Hello everyone, first of all I wish you a good start to 2021.

I'm not used to intervening on a forum, but rather skim over them in order to find a solution. However this time I can not find much about it ...

My question is:

I am testing with ESP8266 in mesh communications using the PainlessMesh library.
It works quite well, each ESP sends messages in string format and they are well received that's all other ESPs.
It would therefore be interesting to be able to generate a broadcast of the same type from an AppInventor app.
This will make it possible to send and receive information from multitudes of ESP sensors and on the other hand send commands to manage remote output actuators located in the mesh network. All without going through the internet.

Thank you already in advance for reading my request.

Library :
Tutorial :

I would like to see the same. I love the way that painless mesh works as it solves most of my multi device problems.