I was never successful in stopping flask adding a nonce value. I don't know if it's something about my version of flask or some kind of environment setting?

Ultimately, the only way I could resolve this problem was to place the URL in a hidden div statement (rather than inline script) and extract it in the javascript code. While this works, it is extremely ugly and a hack. It seems to me there should be a simpler solution. But I don't have the time to look for it. I will leave this question for posterity in case anyone else can shed some light on the subject.