Let's say you've written a check to a client that you've recorded as an 'Offline refund' on a project, but then you need to remove it or edit the amount.

All you need to do to remove an Offline Refund from the project is to first head to your project, then select the 'Billing' tab

From there you'll be able to see your Refunds
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You can Edit or Remove Offline Refunds by clicking the 'Action Dots' associated with the payment, and finally 'Remove or Edit'