apply-a-coupon-minimum-cart-total.php

/**
 * Apply a coupon for minimum cart total.
 */
function wb_add_coupon_notice() {

		$cart_total     = WC()->cart->get_subtotal();
		$minimum_amount = 50;
		$currency_code  = get_woocommerce_currency();
		wc_clear_notices();

	if ( $cart_total < $minimum_amount ) {
		WC()->cart->remove_coupon( 'COUPON' );
		wc_print_notice( "Get 50% off if you spend more than $minimum_amount $currency_code!", 'notice' );
	} else {
		WC()->cart->apply_coupon( 'COUPON' );
		wc_print_notice( 'You just got 50% off your order!', 'notice' );
	}
		wc_clear_notices();
}
add_action( 'woocommerce_before_cart', 'wb_add_coupon_notice' );
add_action( 'woocommerce_before_checkout_form', 'wb_add_coupon_notice' );