Wow, so I started this process about 5 months ago!
Shopify requires you implement their Billing API if you're a paid app for all your users which doesn't fit my business model since not everyone needs to integrate with Shopify when using Trunk. So I had to first get a billing exemption (which took forever) that gave me permission to charge customers with Shopify's Billing API, only if they installed Trunk through the App Store. After getting the all clear, I then had to implement Shopify's Billing API alongside my current Stripe Billing API and have everything play nicely (which took forever).
Shopify is pretty strict on their guidelines so I suggest you make sure you meet every single line item if you're interested in getting listed. After 3 denials and lots of back forth (which took forever), I finally got the approval. Big shout out to Shopify though on making sure only high-quality apps make it on there.
Check it out: https://apps.shopify.com/trunk
Now it's time to get reviews 😱Open to suggestions on this!