This method rejects the posted merchant payout due to various reasons, and this is applicable for 4-eye and 6-eye principle workflows. For payload explanations for both request and response, click here 
using OneKhusa.SDK;
using OneKhusa.SDK.Models.Transactions.SingleDisbursements.Shared;

//code omitted for brevity

OneKhusaResponse<RejectPayoutResponse> response = await client
    .Transactions
    .SingleDisbursements
    .RejectPayoutAsync(new RejectPayoutRequest
    {
        TransactionReferenceNumber = "260219YXF882",
        MerchantAccountNumber = 12345678,
        ReasonForRejection = "The beneficiary is a defaulter",
        RejectedBy = "joe.doe@example.com"
    });

if (response is { IsSuccess: true, Data: not null })
{
    Console.WriteLine($"Message: {response.Data.Message}");
    return;
}
//it means an error occurred
//Get error details from response.Error
Note: This method accepts custom idempotency key generated by your system. By default, if not specified, it will create one on your behalf.