Inapp billing - Internal test issue

What I did until now:

-I have created developer account and merchant account.

-I have compiled the code by using "Generate Signed Bundle/Apk" where I created the new Key

-I have created the new listing for a test app in Internal test, uploaded app bundle, and status is: "Available to internal testers "

-I have created SKU for 1 month subscription

-I have added my test email in list with testers

-I have added my email in the list with License testers and set option "Licensed"

-I got url for downloading test app... which at the moment shows " We're sorry, the requested URL was not found on this server. "

but ok, i guess that it is as stated... that it can take up to 48h for first time published app to become available to testers...

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What I dont understand now is this:

In few hours it will be 48h since i did all that. But all this waiting is kinda making me paranoid a little bit :)

-Does Google have to approve new developer/merchant accounts? I didn't find any notification about that in Play console

-Does Google have to approve app even for internal test?

-Am I able somehow to test inapp billing by installing Signed APK directly on my phone? Or i can test it only by downloading app directly?

-Also I compiled Google's Trivial Ride example inapp billing app, installed on the phone and i can purchase Google's test subscription.. So I guess that it is possible to test inapp billing with offline installations... Just i dont know if it is also possible for my app.. or Google did some special thing to make it available for their demo app.

I have tried to cheat... by adding a new button in the Trivial Ride, which then opens new activity which runs my billing code for subscriptions.. and it works. With my code I can purchase those Google's test subscriptions... But when I compile my own APK (signed with the same key i used for uploaded app bundle), then returned list with available subs is empty.

Soo... Any opinion? :)