Improve 'bad request' error message. #1536
Description
Originally brought up here: #1531 (comment)
The error message is "Failed to read request" which sounds too much like it's a server-side error; when in fact, it's a user error (malformed query).
We're not sure whether this can be changed, or if so, how much effort it is. But would be good to change this to something that makes it clearer that the user needs to fix something in their query.