To help trouble shoot, I'd like to get some additional information ... which case applies to what you're trying to do?
Are you trying to preview content before publishing in DPS 2015 (e.g. create a preview app to view all content - collections & articles)?
Are you trying to view articles in your own app (e.g. not a preview app)?
Are you trying to view the metering experience within the app (e.g. viewing paywalls, purchase options, etc.)?
There are no settings in DPS Classic that would cause this "not available" situation. If you could send screenshots of your content and collections list views of the article your'e trying to view and the collection that the article belongs to, that will help with troubleshooting. Also, check to make sure that there are no errors and let me know what the publishing status says (I can also view that in the screenshot)
Note: The default article access in DPS (classic) was protected. The default article access state in DPS 2015 is metered. Migrated content will keep the original article access state - this state does not change with migration. You can change the state in the Article Properties in DPS 2015. If you enable the "publish all collections as free" this only applies to new collections published after the default setting is enabled. Again this not apply to migrated content.