<?php
/*
URL: https://wproot.dev/blog/get-woocommerce-current-product-category-single-product-page/
*/

if ( has_term( 'tshirts', 'product_cat' ) ) //product category is tshirts
{
    $flatrate = '10.00';
}
elseif ( has_term( 'hoodies', 'product_cat' ) ) //product category is hoodies
{
    $flatrate = '15.00';
}
else
{
    $flatrate = '0.00';
}

echo 'USD'.$flatrate.' Flat Rate Shipping';
?>