[Solved] Testing In-App Purchase products before app submission?

My game will be released as a free demo with an In-App Purchase to unlock all waves. I've integrated the Unity Purchasing plug-in, and I've set up all banking and tax info through iTunes Connect. I added a non-consummable IAP product in iTunes Connect, with Product ID matching the string I use in my code.

According to Xcode's console, I'm able to connect to the iTunes store, and the game receives products from iTunes. Problem is, the purchase process fails even before I confirm using my sandbox tester account. Even worse, all it gives me is the wildly unhelpful error message "PurchaseFailureReason: Unknown".

The error message has already been logged by the time this popup appears, with my own "purchase failed" dialog behind it.



iTunes Connect says, "Your first In-App Purchase must be submitted with a new app version." Just in case, I filled out all metadata on the product page, since Xcode was complaining about missing metadata and asking if the product had been disapproved by the App Store. I no longer get that console message, but sandbox purchasing fails anyway.

I've seen other threads asking about the same iTunes Connect notice, but nothing that seemed conclusive. Am I testing in the right way? I don't mind opening a TSI, I just want to make sure I've got the basics covered before I use one of two TSI requests on this.

EDIT: This is mysteriously working after no code changes. I'm going to chalk it up to my iTunes Connect account misbehaving.