I got it fixed, not sure how. I have contacted shopify theme for my website. They were very helpful. They assured me that the code is correct.I spoke to Google merchant centre. They told me to fix some code in shopify. I went back to shopify. They wr...

Thank you Ilana, you are very helpful as I'm still getting warnings from Google for products with variations. I will try and contact the theme provider if they can help and also send you an email for your suggested help.

Thank you for your explanation, now I understand what google means by mismatch and the URLs. But how do I fix the theme? there are no options for me to add more data or different data to be added to the URL for different sizes