The Google Feed is uploaded by FTP every night at approximately 6 am UTC.
You need to set up an FTP account in the Google Merchant Center and you need to put the same username and password into your Webstore Manager on the Nitrosell Portal.
First go to The Google Merchant Center Dashboard
Click on Settings to expand it and then click on FTP
You need to choose an FTP username and password.
Then on the Nitrosell Portal, choose Products and then Product Feeds and Select the Google Merchant Center.
Google Feed Config on Nitrosell Portal
You enter the same username and password in here -
Search for Google Feed on this forum for more information on configuring your Google Feed