2 answers

Hi Amit,Sorry for this issue that you're encountering.Can you please double check that your Developer Edition Org does not have any namespaces setup in it?Trailhead does not support namespaced DE Orgs and so if you have a namespace registered for the DE Org, you'll need to sign up for a new one and complete this module there.When trying trailhead, we encourage users to create new Dev Org's such that the previous config changes do not affect the trailhead challenge settings.To login into trailhead you can use your old org but for activity(code and config) related changes you can use new org. In such a way all point will add in your old profile only. Please check the below link for help.
Please mark this as solved if the information helps.
Regards,Nagendra.