Partial success with the Chrome InApp purchase flow within a Chrome extension. I have included the buy.js file and implemented the flow as listed on the Chrome walkthrough here:
I have had successful payments even from other random computers. You may have to check follow for the potential fix:
Make sure In-app Items are enabled for all, not just yourself or test users
Make sure to use 'parameters': {env: "prod"}, wherever you are making "google.payments.inapp.*" calls
Make sure users are Signed-in their browsers in order to get items, licenses and make final purchases successfully
Make sure to use the originalId(nmmhkkegccagdldgiimedpiccmgmieda) while calling chrome.runtime.connect() in buy.js, if not then it is the place where it triggers INTERNAL_SERVER_ERROR.
Hope it helps.