I saw this happen with someone recently who was having the same issue with data not showing up online and getting the 504 response code. Turns out it was a missing UUID in the list of sensor variables in the Arduino sketch. When there’s a mismatch between the string you send Monitor My Watershed and what it’s expecting, you get the 504 response. I can’t see the original string that was posted before Sara edited to remove the UUIDs, but it appears that there’s a UUID missing from the string right before the last parameter (which I’m guessing is cell signal percent?)
So make sure there are the same number of parameters in the sketch as what the website is expecting, and that the sketch code in the two sections that deal with the UUIDs and parameters are matched up properly.