James, you mentioned you have an ArcGIS Online subscription. Do you know what type of account it is? Are you a member of an organization, using a single developer account, a public account, or something else? If you are a member of an organization, has your administrator given you access to publish and edit feature services?
I am a member of an organization and have all administrator permissions.
Can you provide the steps you took to create the Map Tour?
- Did you start from by sharing a web map or from the story maps website?
- Did you do anything in the map tour builder before trying to select the source for your images?
I started from this url:
https://www.arcgis.com/apps/MapTour/index.html?fromScratch
James -- is it possible you are logged into ArcGIS Online using another (public) account? Try going to www.arcgis.com and logging out, then log back in using your organizational account and create a Map Tour from the My Content page (Create > App > Using a template).