I've checked trailhead and can't seem to find a solution to an error I'm getting when trying to create an approval process that validates when a prospect account becomes a customer in trailhead. "Challenge Not yet complete... here's what's wrong: 
There was an unexpected error in your org which is preventing this assessment check from completing: System.DmlException: Process failed. First exception on row 0; first error: NO_APPLICABLE_PROCESS, No applicable approval process was found.: []"

If you have any ideas, please let me know. Thanks!

Here's a screen shot

Here's my diagram: