Error message when trying to do my "Admin. Cert. Maintenance". When trying to access the "Mi Trailhead Playground 1" on the 2nd topic (Get Hands-on with Related Object Fields on Dynamic Forms)

Error message when trying to do my "Admin. Cert. Maintenance". When trying to access the "Mi Trailhead Playground 1" on the 2nd topic (Get Hands-on with Related Object Fields on Dynamic Forms).

I am trying to maintain my Salesforce Admin Certification. 

This requires the completion of two chapters in Trailhead. 

I passed the first chapter but when trying to complete the 2nd chapter (

Get Hands-on with Related Object Fields on Dynamic Forms)

I hit an error message. When clicking on the "LAUNCH" button to access the "Mi Trailhead Playground 1" I get following error message: 

Please advise how to get this fixed. Thanks