I am looking to integerate IAP (https://developer.chrome.com/webstore/payments-iap) in to my extenstion but I can't seem to find a way to test payments.
If I switch the env to sandbox I get and error of type "ENV_NOT_SUPPORTED_ERROR"
Quoting the docs you link:
Testing purchases
Prior to publishing your app to the world, you can test the In-App Payment experience by publishing it only to trusted testers. When your app is published to trusted testers, the purchase flow will proceed normally, except they will not be charged.
来源：https://stackoverflow.com/questions/28311236/testing-chrome-in-app-payments