I'm trying to complete a challenge, but the Playground is giving me an error, as shown in the image below. Who should I contact, or how can I resolve this issue?

Hi , 

Meanwhile I found the cause.

It seems that there were a few orgs linked to this Trailhead Challenge.

The one that was attempted to be launched was expired.

After spinning up a new org, it worked.

My product suggestion would be to include this in the error message that is displayed to the user.