Are you are using a "rating" plugin? Try disabling any plugins as they sometimes do cause an error to appear or missing fields.
To find out exactly what's wrong, go to Google and search for their "Structured Data Testing Tool". That's what you need to do. It will show you exactly what the problem is and how to fix it.
You'll need to work with a developer to get such schema fully implemented on your theme.
aggregrateRating can be ignored if you don't have a reviews app install. Most review apps do not do "review" schema so that can be ignored. Other values can be quickly done.
Another option is to use a json ld schema mark up app. You can have this inserted in-tandem with whatever schema is already there as Google will give precedence to the most complete, error-free schema source.