Hello,
I tried many times... but receive the same error message : "Challenge Not yet complete... here's what's wrong: 
Formula in custom field 'Account Annual Revenue' is not correct. Check the instructions."
I followed all instructions & get the right results. It's a basic & very simple formula.
Do someone else encounter the same issue ? Any solution ?

I'm doing the simple lightning components challenge and have hit this problem in my existing trailhead org and a brand new dev org that I've just created:

Challenge not yet complete... here's what's wrong: 
There was an unexpected error while verifying this challenge. Usually this is due to some pre-existing configuration or code in the challenge Org. 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: QVWBQHAG