When calling the stack.sync API, I get an exception which is reported as...

The promise rejected with the reason "#".

Here's a screenshot of a debugger showing the failing line within the minified code of the project running my test case.

See https://gist.github.com/joepie91/04cc8329df231ea3e262dffe3d41f848#why-its-unnecessary-to-include-minified-builds for some reasoning that suggests the contentstack package should not be minified before distribution via NPM given it creates problems like this for no reason.

See also e.g. https://www.briefs.fm/3-minutes-with-kent/221 for more explanation. I have no idea why it's minified and it makes debugging it near to impossible.