Which constraints am I missing on my native messaging hosts for my Firefox extension in Linux?

I have a Firefox extension calling a native messaging host on Linux (CentOS 8 Stream); here is the declaration of the host :

  "name" : "myhost",
  "description" : "My Host Description",
  "path" : "/home/benoit/my_app",
  "type" : "stdio",
  "allowed_extensions" : [ "myhost@mydomain.com" ]

my_app is a simple executable file (chmod 755), created with account root, than opens the notepad (/usr/bin/gedit)

However, this doesnt work and I get the following error from the firefox console:

Failed to execute command "/home/benoit/my_app"
    startupPromise resource://gre/modules/NativeMessaging.jsm:113

The surprising part is that if I use the actual binary of notepad directly

"path" : "/usr/bin/gedit"

it opens a notepad successfully.

So I tried moving my_app to /usr/bin/my_app, with the same permissions as /usr/bin/gedit, still under root account, but I again got the following error in the firefox console:

Failed to execute command "/usr/bin/my_app"

Quick note: my_app is working fine when testing with another test Chrome extension.

I feel like I am missing a setting or a constraint somewhere, but I have no idea what it is. Any thought?