Thank you for your request.
First, we specify the value of the global variable.
We won't be able to see this variable in Preview.
But you can test it in the web integration to which this chatbot is connected(If this chatbot is not used in the web integration, then I advise you to create a web integration and add this chatbot to it for testing. I will show how to test in the web integration, but you can also do it from other integrations.)
Go to the "Chat page" tab. On this tab, you can test your chatbot and you will see that the variable is coming.
Please note that currently the variable on will not work if it looks like this "my-glob-var". It can look like this "my_glob_var", "myGlobVar", "myglobvar".