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Select Disbursement / Recovery Items; this will open a full list of Purchase Items from which you can manually click on each item code individually to edit.
In the default notes field, type what you would like to auto-populate into the description field of a Disbursement Payment. This can be manually edited when making a payment - hence you can use this feature to guide users as to what you want entered into this field.
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Note that you can still bill this disbursements at any point.