Cannot get my app approved because of error "Can not connect to iTunes"

I read many answers here with similar problems but none helped me to get my app approved. It's been 3 weeks of trial and error. I am totally frustrated of it.

What I am trying to do:

I am submitting my first app (there is no other app with my account created yet).

I have one in-app purchase (nonconsumable) in my app that removes ads and opens all content.

Sounds easy right?

I have been rejected for a few different reasons that has one thing in common - they (Apple testers) cannot successfully perform in-app purchase.

What I did:

  1. Successfully bought and restored in app-purchase with my sandbox user.
  2. At first I was using swifty storekit library. Got refused with "Unknown error. Please contact support" So I ditched this library and Implemented whole code myself, according to apple documentation.
  3. As I read there can be problem with my agreements, tax and banking settings in Itunes connect - found out that there was red line about transfering my account settings (dont remember exact line) - did dissapear after 2 days by itself as I read in some answer here. There is no problem there now.
  4. Did find out that I must wait some time before in-app purchase starts working. I takes about 2 days to in-app purchases start working with testflight user, so waited until it starts to work - then successfully bought in-app purchase and restore also works fine even with testflight testing account. (again got refused)
  5. there is not exactly stated how to submit first in-app purchase ever, it is just said submit with binary. I did not get this at first, found out that I should not send in app purchase by itself, but I should "append" my in app purchase in the same form as I am sending my app. At first I tried to send my in app purchase in its own formular. But then I got rejected with error "We found that while you have submitted in-app purchase products for your app, the in-app purchase functionality is not present in your binary." (I say it again - there must be api there as I can successfully buy app with test account).
  6. read in some other answer that I can ask to get my in app purchase approved, so I write "please approve my in app purchase - they did, but I got refused.
  7. Now I cannot select this in app purchase with my binary, as it is not shown for selection probably because it is already approved. So I did submit app without it and got the "in-app purchase functionality is not present in your binary" error again.
  8. Created new in app purchase, this one can be selected to be submited with app. Got rejected again, with error. "can not connect to iTunes"

In app-purchase is then switched to "Developer Action Needed". This is probably a good thing as if they would approve it then I could not select it with binary as it would be invisible.

What else should I try? What to change? Where to look? I am totaly lost. 3 weeks of time lost. As I cannot reproduce the problem I cannot solve it. Programing is easy, but to get app approved looks like imposible.

Few of many many visited links:

In App Purchase functionality is not present in your binary
iOS In-App purchase works in development but not in production