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Hello,

Rank Math takes the schema data from your product pages automatically and turns it into Schema-ready content. Likewise, the aggregateRating and review fields are taken from your actual product reviews that your buyers/customers leave on your products.
https://i.rankmath.com/Ni50EF

If you don’t have any reviews yet, that is going to show up as a warning in the schema testing tool. That’s because Google will actually look for those fields.

Please acquire some reviews and ratings to get rid of the aggregateRating and review warnings.

You can fix the SKU and availability issue quickly as well: https://i.rankmath.com/wtM5aM

To fix the brand warning, head over to WordPress Dashboard > Rank Math > General Settings > WooCommerce and choose from any of the available fields to use as your product’s brands.
https://pastebin.com/4SMjE228

If you want to use a custom value for your Brands, you can do that by using the following code in your theme’s functions.php file:
https://pastebin.com/JEfTheYn

Replace the “Rank Math” text with your actual brand name then run your website through the Structured Data Testing tool once again.

For the GTIN, ISBN, MPN issue, you can fix it by adding that to your products using the custom product attribute feature in WooCommere or you can use this plugin: https://wordpress.org/plugins/product-gtin-ean-uc-isbn-for-woocommerce/

For the priceValidUntil warning, you have to either ignore that or add a sale price with validity to get rid of it: https://i.rankmath.com/cMqAAH

Hope that helps and please do not hesitate to let me know if you need our assistance with anything else.