In the Mendix Sprintr for you project on the environments page there should be two buttons for a free app: “View live log” and “Show latest build output”.
I’d suggest taking a look at these. If when you deploy it fails during the package build I’d expect to see an error in the build output. If the package builds but the error is deploying to the environment then if you have the Live Log open in your browser (selecting “show all” logs) whilst trying to deploy then it should give you logs and you may see an error here.
I’ve not used free apps much but I think the above still applies.
There was a maintenance scheduled today for the Developer Portal and during that maintenance window, deploying app had some issues. Please try again to deploy your app and see if you can do it without any errors. Make sure to run app locally first and check if there is any errors in the logs. Then Run in cloud.
Mendix status site displays any maintenance schedules and past incidents. You can see details there.