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Gauri Shankar SinghGauri Shankar Singh 

We recommend using a new Developer Edition (DE) to check this challenge. If you're using a new DE and seeing this error, please post to the developer forums and reference error id: WTTTJIEW

I have completed all the task but it gives error that i have to create new playground but I have already used all 10 playgrounds
VinayVinay (Salesforce Developers) 
Hi,

Try in new playground org if you still see issues kindly reach out to trailhead support team.

https://trailhead.salesforce.com/help

Kindly let me know if it helps you and close your query by marking it as solved so that it can help others in the future.

Thanks,
Aravind Y BAravind Y B
Hai,Gauri Shankar Singh
Try to Login With New Org/New Playground Then u not get the error
Gauri Shankar SinghGauri Shankar Singh
Hi @Vinay problem not solved in the playground org
VinayVinay (Salesforce Developers) 
Reach out to trailhead support team who can help you using below link.

https://trailhead.salesforce.com/help

Thanks,