Q:

Conditional custom price suffix for variable products in WooCommerce

I have set the price suffix for all my products in Woocommerce (“per box” in my case). This works for variable products as well as for single products without problems. 
Now I want this prefix to change to “per pallet” for some product variations of a product. I’ve read a lot and tried a lot, but I haven’t found a solution yet that could be applied to individual variants of a product. Can anyone help me?
Below is the Code I tried. There are no error messages, but it does not change the price of a specific id.
add_filter('woocommerce_available_variation', 'variation_price_custom_suffix', 10, 3 );
function variation_price_custom_suffix( $variation_data, $product, $variation ) {
    $args = array(
    'post_parent'   => get_the_ID() // get parent post-ID
);
$variations = get_posts( $args );

foreach ( $variations as $variation ) {

    // get variation ID
    $variation_ID = $variation->ID;

    // get variation price
    $variation_price = $product_variation->get_price_html();

    get_post_meta( $variation_ID , '_text_field_date_expire', true );

}
    if($variation_ID == 732) {
        $variation_data['price_html'] .= "Text after price";
    }
    return $variation_data;
}

Many thanks in advance and many greetings
keved

A:

You are making it much more complicated that it should be and there are some mistakes:

The parent variable product is the $product function argument (variable).
You don't need to make a foreach loop, as you are already in it.
You are not using: get_post_meta( $variation_ID , '_text_field_date_expire', true );
$variation variable is the array of the current variation data (see here)
$variation['variation_id'] is the product variation ID
The parent variable product id(if needed) is $product->get_id()

So 2 posible ways:
1) Targeting all the product variations of a specific variable product:
add_filter('woocommerce_available_variation', 'variation_price_custom_suffix', 10, 3 );
function variation_price_custom_suffix( $variation_data, $product, $variation ) {
    // For a specific variable product ID (and all its variations)
    if( $product->get_id() == 732 ) {

        $date_expire = get_post_meta( $product->get_id(), '_text_field_date_expire', true );

        $variation_data['price_html'] .= ' ' . __("Text after price");
    }

    return $variation_data;
}

2) Targeting a unique product variations ID:
add_filter('woocommerce_available_variation', 'variation_price_custom_suffix', 10, 3 );
function variation_price_custom_suffix( $variation_data, $product, $variation ) {
    // For a specific product variation ID
    if( $variation['variation_id'] == 732 ) {

        $date_expire = get_post_meta( $variation['variation_id'], '_text_field_date_expire', true );

        $variation_data['price_html'] .= ' ' . __("Text after price");
    }

    return $variation_data;
}

Code goes in function.php file of your active child theme (or active theme). It should better work now, but you will need to complete it to use your custom field.
Related: Adding custom text to the variation price in Woocommerce

