It looks like you have a GUID in the URL for AppID in your POST request, but the documentation says this should be the subdomain name of the app.
https://docs.mendix.com/apidocs-mxsdk/apidocs/build-api/#start-building-deployment-package
You can find the subdomain AppID to use for this by using the Deploy API.
https://docs.mendix.com/apidocs-mxsdk/apidocs/deploy-api/#list-apps
Hope this helps.