Woocommerce if use a specific gateway, then set the value [closed]

I want to add a filter or an action for the plugin, the purpose is to set the value to "0" if the order used "myCRED" gateway.

I found those 2 related filters of the plugin,

uap_filter_referral_amount uap_public_filter_on_referral_insert_amount_value 

actually, I am not sure which one should I use, but I tried both of the 2 filters, when checkout it shows internal error, I think the code may have some error, any one can help?

Here is the code I have tried:

function exclude_mycred_gateway( $  order ){     $  payment_title = $  order->get_payment_method_title();     if ( $  payment_title ) {         $  payment_title == "myCRED";         return "0";     } }  add_filter( 'uap_filter_referral_amount', 'exclude_mycred_gateway');