Hey @petit-ricard,
Here is a regex string that will work:
[^,]+
Also, because you are retrieving a list of channel_name’s rather than just one, you also need to insert a comma between all those before you run the regex. You use :join with “,” (just type a comma, the double quotes will be added for you.)
Here’s what it looks like:
Which turns this:
Into this:
Hope that helps!
–Ken
Looking to accelerate your app development?
Development of Advanced Apps at https://uniqueideas.com or schedule a free intro session 
Ken Truesdale
LinkedIn