Trail error while checking the challenge

Hi !

I am getting below error while checking the challenge in trail mixes.

 Challenge not yet completed in the Developer Edition

But, it is completed. I am getting below other error messages.

1)XXXXXXXXX-dev-ed.lightning.force.com’s server IP address could not be found. 2)Your org is not found. It is been used by another user. 3) you have no accounts connected.

I tried reconnecting dev edition org. Disconnect for org is not available.

Please help me resolve this issue so I can continue with my trailmixes.

Thanks much!