Inappropriate method used

Hi WPClever team,

I found what appears to be a compatibility issue in WPC Shared Stock (v1.1.5) when used with WooCommerce (10.9.4) variable products.

When a variation is assigned to a shared stock group, it becomes non-purchasable on the frontend. The product page shows “Please choose a different option”, and the variation JSON (data-product_variations) contains "is_purchasable": false, even though the variation is enabled, has a valid price, and the shared stock group has available stock.

After debugging, I found that the plugin checks the variation’s visibility using is_visible(). Replacing this with variation_is_visible() in /includes/class-frontend.php:134 resolves the issue, and the variation becomes purchasable again.

It seems variation_is_visible() is the appropriate method for checking the visibility of product variations in this context.

Could you please review this and include a fix in a future release?

Thank you!