Why does my app name change to 'dropit-3' after OAuth redirection?

Ok, I’m developing a public app with the name called dropit (unlist app), then start ngrok and my local server by using** @Shopify_77 /koa-shopify-auth**.

Everything is fine when I’m developing the custom-app: I can install, the OAuth process is fine, redirecting back to the app is fine.

Then I create a public app, I can install that public app in my dev store, the OAuth process runs with no problem (as I get back all offline access tokens and save them back to the database). But I got the 404 when it redirects back to the app URL. I can’t figure out what’s the problem, the same backend has the same logic.

Until I find this funny thing:

So after the OAuth, it redirects back to https://dropit-public-app-testing.myshopify.com/admin/apps/dropit
that should be correct!!! But I got 404 (screenshot attached).

But if I click the apps in my store, and then click the **dropit** (just installed), shopify redirects to this URL:

https://dropit-public-app-testing.myshopify.com/admin/apps/dropit-3

And I can see my app. The question is why **dropit** (app name) becomes **dropit-3** ???