So you’ve paid out for a purchase from “agent 2” and you are now being reimbursed by your customer for the cost of this purchase? In that case you could use the re-billing feature - select the tickbox for the relevant purchase in your list of all purchases, choose “more options” then “rebill to client”. Leave the “markup” at zero and select “contra expenses”. This will create a new sales invoice for the same amount as the original purchase against which you can log the £400 payment received, but in your profit and loss it will cancel out the original purchase rather than showing the same amount as both income and an expense.