I tried this and it didn't work, and I'd already followed other instruction on how to integrate Swift into an Objective C project. Thing is, I absolutely trust The Eskimo so I knew the problem was my end! So many things happening in my main project so I set up another with the same identity such that I could test. But when I was doing so there was one setting in the guides I couldn't remember off the top of my head I just ignored it. Got everything else set up, and Boom, it was working. Told you I trust The Eskimo! Went looking for that setting and changed it back on my original and Boom it's able to call the Swift correctly too. Trust The Eskimo! That setting was "Define Module" and keep it set to No. There are other parts that you need to set up in addition to this one part, and the other thing I'd say which may help you is using the notification centre to go from Swift back to Objective C. That you can get calls back when you have success in your StoreKit classes.

I had this problem too on the simulator, but going back to 18.1 it worked fine. My app is mainly Objective C with calls to Swift to do the app transaction calls since StoreKit 2 is only for Swift. I solved it for 18.2 by going in to the storyboard and looking at the transitions from my main screen to the purchase screen. In there I changed the segue Kind to "Present Modally" and also for the Presentation to be "Over Full Screen". If you do these two settings it then works fine, or at least it did for me.