title: Enhanced E-commerce with Measurement Protocol
body: <p>I have a subscription model and want to track the monthly payments with a server-side call through the Measurement Protocol.</p>
  
  <p>The problem now is that I don't know how to build the call because as the documentation states I need a productIndex which I don't have (at least I think so). Here is the documentation: <a href="https://developers.google.com/analytics/devguides/collection/protocol/v1/parameters#pr_nm" rel="noreferrer">https://developers.google.com/analytics/devguides/collection/protocol/v1/parameters#pr_nm</a></p>
  
  <p>From where does the ProductIndex come from? Or is it unimportant anyway?</p>
  
  <p>Please help!</p>