Hi guys, how can I get a group name?

I can't find information on Google and I'm also a newbie to Moodle. I'm following this: https://tracker.moodle.org/browse/MDL-55358 tutorial, but I can't find the correct custom parameter.

I have the following in the LTI tool configuration:

And I have the following group:

I want to get custom_mygroups = Group_2 but I am getting custom_mygroups = 2.

Thanks in advance!