App failed after initialize

[ChristianOrgs]

Hey lads,

so what I did is setting up a repo, circle ci, firebase which works like a charm. It was kind of a struggle to setup all this to a running environment but it works. I also setup the Shopify app and whitelisted following routes:

https://yxz.firebaseapp.com/
https://yxz.firebaseapp.com/callback
https://yxz.firebaseapp.com/auth
https://yxz.firebaseapp.com/api/activate-charge
https://yxz.firebaseapp.com/api/graphql

I wasnt sure what to whitelist so I decided to whitelist every route there in the beginnig.
What I can do is to install the application and setup billing plan. But if I run the app in my store(free plan dev store) itself I just get screen that: "the requested site couldn't be found". I checked the given redirect URL which seemed to be valid:

https://xyz.myshopify.com/admin/apps/my-app-xyz?token=xyz&shop=xyz.myshopify.com&expires_at=1573638842624&uid= xyz.....

I thought alright have a look in the firebase log. I see that the callback function run trough and run like expected. Also the db will be updated with a new token. I also see that the function response is a 302 for redirect.

Which will be caused in index.js/callback:

return response.status(200).redirect(redirectUrl)

But directly after that a error will be dropped:

Unhandled exception
HTTPError: Response code 422 (Unprocessable Entity)

If I fixed this with a additional else after the first var check in callback function ( Guess this will be caused after function got return the return will be called again from the first if clause ) It runs trough without error. But I still doesn't redirect in Shopify. And I have no clue why.

Might it be a missing whitelist ?
How should the redirect whitelist look like with the standard application ?
I appreciate any help and thanks for this great project !:)
Cheers!

Edit:
-Firebase pay plan is blaze-as-u-go
-Webhooks also set in Shopify
-Tried Shopify API Version 2019-04 & 2019-10