Google Merchants Checkout URL

Hi all,

I am trying to link my Wix store to google merchants and finally as a last part google is asking me to Add checkout to your listings on Google,
As per google this should be like “https:// checkout?I tem_id={id}” but if I write the checkout like this they won’t accept it.
Could you please help me how to address the checkout on google merchants so that I can finalize with this,