How to test an IAP in the sandbox on an Apple Watch

Hi all,

I'd like to test the purchase and restore code I've written for an IAP for an Apple Watch app. The (physical) phone that the (physical) watch is paired with has a sandbox user logged in in the App Store settings. Whenever I try to buy the IAP I get the following error screen:

Any suggestions on what I should be doing? Is it possible to test an IAP purchase with a sandbox user on an Apple Watch app?

Thanks,

Russ