Example of how to show only a 'check' payment method if any of the tickets have the string 'check' within the ticket name

example.php

<?php //Please do add the opening PHP tag if you already have one.

function tw_ee_only_check_payment_method_based_on_ticket_name($payment_methods, $transaction, $scope) {
    //Double check we have a transaction object.
    if ( $transaction instanceof EE_Transaction) {

        //Initialize an array used to hold the ticket names.
        $ticket_names = array();

        //Loop over all registrations and add the ticket name for each reg to the ticket_names array.
        foreach( $transaction->registrations() as $registration ) {
            $ticket_names[] = $registration->ticket()->name();
        }

        //Loop over ticket_names, if any of them have 'check' in the name then pull a check payment method and return only that.
        foreach($ticket_names as $ticket_name){
            if (strpos($ticket_name, 'check') !== false) {
                $check_payment_method = EEM_Payment_Method::instance()->get_one_of_type( 'Check' );
                if( $check_payment_method instanceof EE_Payment_Method) {
                    $payment_methods = array();
                    $payment_methods[] = $check_payment_method;
                    break;
                }
            }
        }
    }
    return $payment_methods;
}
add_filter('FHEE__EEM_Payment_Method__get_all_for_transaction__payment_methods', 'tw_ee_only_check_payment_method_based_on_ticket_name', 20, 3 );