Hi,
Take a look at mine prepare command.
I am doing pretty much the same except I left the icons and the splash screen out.
To save build time on AppCenter use --platform android or --platform ios.
native-builder.exe prepare
--java-home "C:\Program Files\AdoptOpenJDK\jdk-11.0.3.7-hotspot"
--mxbuild-path "C:\Program Files\Mendix\8.7.0.1476\modeler\mxbuild.exe"
--project-path "C:\Users\Contacts\Contacts.mpr"
--github-access-token "XYZ"
--appcenter-api-token "ZZZ"
--project-name "Contacts Native"
--app-name "Contacts Native"
--app-identifier "com.mendix.contactsnative"
--runtime-url "https://contacts.cfapps.eu10.hana.ondemand.com/"
--mendix-version "8.7.0"
--platform android