When viewing the run-log for a failed flow, it would be really helpful to tag or highlight the parameter causing the error in the step that failed - perhaps change the background colour to red, or put a pop-up user-friendly description of the error on an error icon against the parameter.
Having to hunt through JSON code when you don't really know what you should be looking for is very chancy.
Also, putting out error codes like "502 badgateway" is a bit meaningless - why is it a badgateway? Is that a transient or permanent error, and what do I need to do to fix it?
This type of error message looks just like the error codes we used to get out of IBM Assembler 360 40 years ago... surely you can do better than that, Microsoft?