Hide checkout fields for variable product

Change:

$product_id = $product['product_id'];

to:

$product_id = ! empty( $product['variation_id'] ) ? $product['variation_id'] : $product['product_id'];

Thanks! Worked like a charm. For anyone looking, the spot Mike refers to in the code is here:

// Loop through cart products
  foreach( $products as $product ) {

	  // Get product ID and '_virtual' post meta ----the code goes under here---
      $product_id = ! empty( $product['variation_id'] ) ? $product['variation_id'] : $product['product_id'];