Dear Shopify Partners and Developers, all unpublished shopify apps can't be installed anymore like shopify statement below,
"Compliance cutoff dates are quickly approaching to get your app listed in the Shopify App Store in accordance with our new Partner Program Agreement. Be sure to submit your app as soon as possible to avoid reviewal delays-it usually takes our partners several weeks to complete the review process. Please check your dashboard notifications and email to find your cutoff date."
With detailed information on the following link,
What do i need to do?
You just need to publish the app to Public but you can just make sure not to list it on Shopify App store visibility to make sure it won't be available to public.
What will happen is that once the App was published our review team will start reviewing it, All apps must be reviewed and approved by the App Store review team, but you can control your Public app's visibility to be either Listed or Unlisted on the App Store.