I had previously manually setup Google Products about a year and a half ago but am always having problems with my feed-- Google changes things so often it's hard to keep up. And Google Merchant Center doesn't give you many options to manage your product listings, or for that matter explain to you why there's problems or even notify when there are problems. Following the recent changes to Google regarding custom made products needing to have "identifier_exists" attributes set to FALSE, I thought I had fixed everything so I wouldn't have a problem (I only have about 30 products fitting that category). But then, of course, my products all suddenly went inactive two days ago. I tried on my own to fix the issues, but still couldn't get them active again. So as a last resort, I downloaded this Google Shopping App. It worked like a charm! It was able to understand I already had a Google Merchant Account and Google Product Listing Ads (I just needed to click for it to 'check' for it on that step). It was easy to set up, and in simple terms informed me when there was an error, exactly which products were causing the error, and how to fix it. It turned out there were only about 10 products that were causing my whole product inventory to be inactive. I noticed someone previously stated it only publishes 250 products; I don't know if that's been changed, but all of my products were uploaded (over 400).