Google Shopping Shipping Setting

My website is listed in Google Shopping free listing, I received a warning email "The shipping costs in your product data don't match the shipping costs on the checkout pages on your website.""If the issues aren't resolved by the deadline, your Merchant Center account will be suspended and your Shopping ads will no longer appear on Google."
The website is built by OpenCart, the shipping extension is Fastway API. I need someone to set it correctly and get approval from Google in one week.