I developed the app and published in Google Play Store. It's developed in ionic 2 + angular 2 + firebase. It is possible that to accept the payment through Shopify?
I did not use any API of Shopify to develop my app. It is independent from Shopify.
Shopify is an e-commerce platform. Shopify itself does not process payments. I would look into something like Stripe, PayPal, or Google Pay to offer payent processing for your app.
I configured stripe powered by Shopify. I want to say, is there any API to accept payment through Shopify