restrict payment gateway based on coupon code

functions.php

add_filter( 'woocommerce_available_payment_gateways', 'conditional_available_payment_gateways' 20, 1 );
function conditional_available_payment_gateways( $available_gateways ) {

    if( is_admin() ) return $available_gateways; // Only for frontend admin
    
    $coupon_code ='cod';

    if ( WC()->cart->has_discount( $coupon_code ) ) {
        unset( $available_gateways['cod'] );
    } 

    return $available_gateways;
}