Wordpress. Woocommerce. Action hook BEFORE adding to cart
A bit late, but I think you are looking for add to cart validation, which is filterable. Here's an over simplified version:
function so_validate_add_cart_item( $passed, $product_id, $quantity, $variation_id = '', $variations= '' ) { // do your validation, if not met switch $passed to false if ( 1 != 2 ){ $passed = false; wc_add_notice( __( 'You can not do that', 'textdomain' ), 'error' ); } return $passed;}add_filter( 'woocommerce_add_to_cart_validation', 'so_validate_add_cart_item', 10, 5 );