Billing Question

Hello,  I have a question about billing.  I took a Master's hearing in October.  They did not want it transcribed, now they do.  I have already sent out a bill for writing time and apperance fee.  It was promptly paid.  Now, I am about to transcribe the transcript.  How exactly would I bill for that?  Do I deduct anything from what was already paid? Any help you all could give me.  I don't need exact dollar amounts, just a method to go by.  Thanks.
 

If this happens to me, I would bill what I normally would for the transcribed transcript and then deduct what they already paid. I would show the deduction on the invoice.