Hi Heath_Carson ,
Please note: I'm not part of MYOB's API support teams, I'm responding as an interested party, not as an authoritative MYOB source.
CORS is usually related to browsers, there's some discussion here:
https://academind.com/tutorials/cross-site-resource-sharing-cors
Postman doesn't care about CORS when you're using the desktop app version, you may need to either change some settings in your browser, or configure some kind of middle-service to handle the responses and provide back CORS compliant responses to your consuming application.
Hope this gives a hint in the right direction, I won't be any help for followup questions.
