Google Structured Data Errors and Warnings
tl;dr; If you’re seeing structured data warnings, don’t worry… these are totally normal.
One of the most common question users of revws module are asking me - why does google complains about structured data? What's wrong with this module? The answer is - google is at fault. And don't worry about it.
Google has updated their structured data in 2019 and this is causing a lot of warnings, and lot of nervous merchants. But remember, warnings are not errors, they are just recommendations. And in this case you can't do anything to make them disappear. In general, you will see 2 types of warnings.
"review" - The review field is recommended. Please provide a value if available.
This warning is displayed because no review has been written for given product yet. It will be fixes as soon as somebody writes one. There is nothing you can do to make this to go away, other than posting a fake review. And we don't do that, right?
"aggregateRating" - The aggregateRating field is recommended. Please provide a value if available.
Again, this warning is related to the fact that no review has been posted for the product. With zero reviews it's not possible to calculate average / aggregate ratings. Allowed value for review average field should be in range 1 to 5. But with zero reviews, the average is... well, either zero or infinity. If we try to enter zero, google will complain (this time it will be error, not warning). If we enter some valid number (for example 5), google will once again complain that there are no associated reviews. And possibly penalize you for lying. That can really hurt your SEO.
The only correct way to handle this situation is to omit aggregateRating completely. Google will complain with this warning, but it's harmless. Once somebody submit review, the warning will disappear.