Fix Woocommerce issue with USPS and -100% Price Adjustment.

gistfile1.txt

function find_free( $rates, $package ) {

        // Make sure  rate is available
        if ( isset( $rates['usps:D_FIRST_CLASS'] ) ) {
       
        // Go ahead and change the label to display something as $0.00 dollars does not populate. It just says USPS by default.     
        $rates['usps:D_FIRST_CLASS']->label = "USPS - FREE SHIPPING";
     
        // Set the cost to 0.
        $rates ['usps:D_FIRST_CLASS']->cost = 0;
        }
        return $rates;
}
add_filter( 'woocommerce_package_rates', 'find_free', 10, 2 );