SharePoint Site in Custom Team App

I created a Custom Teams App in Developer Portal to access our Learning Site in SharePoint, so that our organization can access the resources while staying with Teams.  However when I go to Preview we can't get a preview.  Our organizations has it set that Custom apps have to be approved before publishing but shouldn't I be able to preview first before requesting publishing approval?  Not sure what we are missing to get preview to work.  Any help with making this work would be great.