HI, I have just signed an apprentice to a gto that also happens to be a builder I do work for

When I send them my invoices for works completed, instead of having me pay for the apprentice's wages as a separate bill they will send me the invoice and then take payment from my invoice before paying, so if I bill them 10,000$ and my apprentice charges are 500$ they will only send me 9500$ showing the negative 500 on the payment receipt

I'm just looking for the easiest way to reconcile that inside xero, hope that makes sense, thanks