Google Search Console shows errors in some properties in web pages

I indexed my site by Google search console but it showed errors in some pages where my products are shown. foe example "Invalid enum value in field "availability"". When I checked my page source, the error is for this part

    <span itemprop="availability" href="http://schema.org/InStock"/>1000</span>

As you see, it is a positive number. This error shows for some pages but not all.