I suggest the following change on the Google Shopping plug in in the Plugins/Nop.Plugin.Feed.GoogleShopping/GoogleShoppingService.cs file:
From:
//link [link] - URL directly linking to your item's page on your website
var productUrl = $"{store.Url}{product.GetSeName(languageId)}";
writer.WriteElementString("link", productUrl);
TO:
//link [link] - URL directly linking to your item's page on your website
//If SSL enabled use secureURL
if (store.SslEnabled)
{
var productUrl = string.Format("{0}{1}", store.SecureUrl, product.GetSeName(languageId));
writer.WriteElementString("link", productUrl);
}
else
{
var productUrl = string.Format("{0}{1}", store.Url, product.GetSeName(languageId));
writer.WriteElementString("link", productUrl);
}