Looks like Challenge 7 is not working for me.. I tried with 2 separated Playgrounds from the scratch and it still fails with weird error, even though I think I've done everything right. I have no idea what else I should try.

Error message:
There was an unhandled exception. Please reference ID: GFXKWRGA. Error: Faraday::ClientError. Message: BAD_REQUEST: Specify a valid value for the source parameter.