In order to successfully submit your app to the Google Play Store and Apple Store there are a few required links that need to be added to the App Store Listing. One of those links is your privacy policy.
If you already have a privacy policy, you can add that link to your privacy policy to your App Store Listing.
If you need a privacy policy, Shopify has a generator that will create a privacy policy for your brand.
You can access Shopify's privacy policy generator HERE