IAP sandboxing IAP failed at 10.3

I have IAP code running from IOS 9.0 with no problem. I upgraded to 10.3 today and can no longer test IAP in a sandbox environment. I am using Xcode 8.3 now. Specifically what's going on:

• list of downloadable products (so the connection is ok)
• the product is added to the payment queue
• GUI prompts for appleID password
• On input I get .failed in from paymentQueue
• then the GUI will display "Accept IAP Purchase" (env. sandbox).
• If I say OK, I get "no connection to the iTunes Store"

Does anyone have similar issues with 10.3?

Please note that my own code has been working without problems since a few months with earlier versions of iOS and that I definitely have an internet connection on my test device.

thank