Redeem or exclude for specific Products

To allow or prevent a gift card balance from paying for specific products, use the pwgc_eligible_cart_amount hook.

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Redeem or exclude for specific categories
Redeem or exclude for products that are on sale

Note: If you are more comfortable adding the code to your functions.php you can do that instead of using Code Snippets.

1. Download the free Code Snippets plugin: https://wordpress.org/plugins/code-snippets/
2. Create a new Snippet with the following code:

function custom_pwgc_eligible_cart_amount( $eligible_amount, $cart ) {
    //
    // Set this to the Product IDs of the eligible products. Remove the numbers if all products are eligible.
    //
    $eligible_product_ids = array( 123, 456 );

    //
    // Set this to the Product IDs of the ineligible products. Remove the numbers if all products are NOT eligible.
    //
    $ineligible_product_ids = array( );

    foreach( WC()->cart->get_cart() as $cart_item ) {
        $valid_product = true;

        if ( in_array( $cart_item['product_id'], $ineligible_product_ids ) ) {
            $valid_product = false;
        }

        if ( !empty( $eligible_product_ids ) && !in_array( $cart_item['product_id'], $eligible_product_ids ) ) {
            $valid_product = false;
        }

        if ( !$valid_product )  {
            $eligible_amount -= $cart_item['line_total'];
            $eligible_amount -= $cart_item['line_tax'];
        }
    }

    return max( 0, $eligible_amount );
}
add_filter( 'pwgc_eligible_cart_amount', 'custom_pwgc_eligible_cart_amount', 10, 2 );

Depending on your needs you can set the Eligible Product IDs to pick a few products that can be purchased, or set the Ineligible Product IDs to block out a few products that are not allowed to be purchased with a gift card.

The code will still allow the product(s) to be purchased, it just prevents the amounts from being paid by the gift card balance.