Resource generations fails with error "HTTP Error 503: POST https://res.ionic.io/api/v1/upload"

This indicates the the installed ionic cli release is outdated. Update to the latest release. The ionic cli version is not related to the framework version. The latest cli release can be used with any framework version.

npm uninstall -g ionic

npm install -g @ionic/cli

After updating the cli you will be prompted to install the cordova-res module.

npm install -g cordova-res

After installing this module the resource generation process will run normally. Review the cordova resources docs to ensure that all source images meet requirements.

error text:

HTTP Error 503: POST https://res.ionic.io/api/v1/upload