Integrate Payment in Shopify App for the Shopify App Store

I am building an app for the Shopify App Store that will have payment integrated for the services. It seems that Shopify has rules on using Shopify Payments to process the payment as it says “cannot guarantee the other methods of payment”. I can’t find any documentation about how to integrate Shopify Payments to an app for the Shopify App Store. To be clear, the app would live both inside the admin as an app and outside Shopify.

  1. Is there really no way to use Stripe?

  2. If need to use Shopify Payments, where is the documentation for apps in the App store and not for stores?

  3. What is standard practice here?