Refund on invoice

I created a refund on an order but it is not shown in invoice?
How can I show refund amount on invoice?

Thanks in advance

Do you mean the PDF invoice or the email ?
For the PDF you would need to modify the routine
        public virtual void PrintOrdersToPdf(...
in nopCommerce42\Libraries\Nop.Services\Common\PdfService.cs

Have a look at how it works then add a new line to print the value of order.RefundedAmount

For the email you could enable the OrderRefunded.CustomerNotification template in Message Templates