This is an issue that we are aware of, it has been fixed and you would need to be updated to the latest release of DPS v.15.4.2 and above.
As a temporary workaround, you can do the following:
Double Click on a relevant posting where the invoice is missing.
Click Edit transaction.
Enter the reference in the Ref field.
Click Save.
Please note - You cannot edit billed transactions (to do this the bill would need to be reversed, to enable the disbursement to be edited, then re-billed again).
To request an update, please ask a question in the MyAccess Portal Digital Assistant and ask to "Speak to a human" to be put through directly to our support team.