We are a fulfillment company with several clients who use a shopify storefront, and would like to write our own custom app to integrate with the API. It would need to send inventory balances, retrieve order information, and send tracking information. We are confused about the differences between a private app and a custom app.
Our company builds these things all of the time.
The two ways you go about it are either to build a public app and do it in a way that configures to each of the stores... or .. you are building a private app that you are deploying individually to each client store.
Public is a lot more work and would be a viable option if you want your app discoverable by the public at large. If you are more enterprise-only or selective in your clients, then private is easier and just becomes part of their onboarding.
What I think Shopify told you ins more about the limitations on their API .. https://shopify.dev/api/usage/rate-limits - however, in your case you are not syncing inventory so it shouldn;t run out those limits like it would for a product feed.
Happy to discuss if you are still looking for this type of work.
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