How to resolve OAuth redirection error during app submission for API integration?

[shpg_dev]

Hey!

I raise a question here as well about the topic, hoping that it will be useful for other developers as well.

We are developing an application that had the functionality for our customers to manage their products on Shopify through our ShopifyAPP, which was responsible for the authentication and auth scopes only.

That APP wasn't published, because it requires having an account on our site, so installing it from an app store is not enough to use it as a stand-alone "application" in your Shopify store.

But... since the 1st of September users can not install unpublished apps anymore, so our newcomers or the old ones with new Shopify stores can not attach their shops to our system.

We decided to accomplish the submission procedure, even though we realised that it describes a much wider, general-purpose application than we have. (It also includes some essential changes like GDPR...etc)

We submitted our app, but we stuck with the process with the following reqests:
"There was an error installing your app. The app must be installed to perform the security check. We expected OAuth to be initiated at https://app-security.myshopify.com/admin/oauth/authorize but were redirected to {REDIRECT_URL}"
The REDIRECT_URL points our account attachment redirect page, where our ShopifyAPP redirects the users after an account attachment, but of course, if you install the APP from the store, it is possible that you do not have an account in our system at all.

How should we resolve that?

• Test account for the review process?
• Fallback URL that can explain what happened, and how can you use that integration?

Thanks!