Accurate geolocation using the Google Measurement API

I am having problems with Google Measurement Api . I need to manually report ecommerce transactions to analytics, and the only data I receive from the payment processor is the country code (which is not accurate enough for our analysis process) and the IP address of the person making the purchase.

We tried to send the uip (User IP override) parameter , but the analytics ignores the IP and does not extract Geolocation from it.

We tried to use geoid , but as I said are not accurate. We also need information about the city. I see that the geoid can take an integer as a parameter that describes the exact location, but I don't know how to get to that number as long as I have an IP address.

Any help or advice would be appreciated.