How do I fix an issue preventing me from completing a challege

I am in the process of completing the User Management: Control What Your Users Can Access module. 

I have completed all the steps. However, when I go to step that requires me to:

• Create a muting permission set in the permission set group and name it Sales User Muted (API Name: Sales_User_Muted), I get the following message when trying to create the required muting permission set: "The API name you entered is already in use. Enter a unique API name."

I didn't create and can't find the API that is supposedly already exists. Also, the challenge won't work with a different name and API name. I've tried to create new playgrounds and get other error messages. 

I've spent 5 hours trying to fix the issue with no luck. Any help would be appreciated.