I have an Article Detail page that was created by another administrator last week. I'm now trying to work with the page to make sure articles are visible, but I keep getting the following error when I just try to go to the page.

NOTE: This is in our sandbox, and we enabled Lightning Knowledge last week as well.

I have an Article Detail page that was created by another administrator last week. I'm now trying to work with the page to make sure articles are visible, but I keep getting the following error when I just try to go to the page.

NOTE: This is in our sandbox, and we enabled Lightning Knowledge last week as well.

I'm having all sorts of problems trying to complete the challenge for the sharing rules section of this module. I feel like I have everything setup properly but still get this error message:
Challenge Not yet complete... here's what's wrong: 
The Sharing Set is not setup with proper Case access. Please check the requirements.

Sharing set name is "Share cases with customers"
Applies to Profiles: Customer Community User
Access Granted: Case - User:Account = Case:Account - Read/Write

What am I missing