This function adds the last payment method selected on a transaction if there are no payments on the transaction.

tw_ee_add_last_payment_method_to_csv.php

<?php //Please do not include the opening PHP tag if you already have one

add_filter('FHEE__EventEspressoBatchRequest__JobHandlers__RegistrationsReport__reg_csv_array', 'tw_ee_add_last_payment_method_to_csv', 10, 2);
function tw_ee_add_last_payment_method_to_csv($reg_csv_array, $reg_row) {
    
    //If this is now a primary registrant row, return and do nothing
    if($reg_row['Registration.REG_count'] != '1'){
        return $reg_csv_array;
    }
    
    //Check if payment method(s) is empty
    if( empty($reg_csv_array['Payment Method(s)']) ) {
        //If payment method(s) is empty, pull the transaction object
        $transaction = EEM_Transaction::instance()->get_one_by_ID($reg_row['Registration.TXN_ID']);
        //Check we do actually have an EE_Transaction object
        if($transaction instanceof EE_Transaction){
            //Pull the last payment method from the EE_Transaction
            //if we don't have a payment method at this point, the user didn't finalize
            //so we set the value to 'Unknown'
            $payment_method = $transaction->payment_method();
            $reg_csv_array['Payment Method(s)'] = $payment_method instanceof EE_Payment_Method
            ? $payment_method->admin_name()
            : esc_html__('Unknown', 'event_espresso');  
        }
    }
    
    return $reg_csv_array;
}