Woocommerce Auto Coupon

auto_coupon.php

add_action( 'woocommerce_before_cart', 'apply_matched_coupons' );

function apply_matched_coupons() {
    global $woocommerce;

    $coupon_code = '10percent'; // your coupon code here

    if ( $woocommerce->cart->has_discount( $coupon_code ) ) return;

    if ( $woocommerce->cart->cart_contents_total >= 500 ) {
        $woocommerce->cart->add_discount( $coupon_code );
        $woocommerce->show_messages();
    }

}