Once an invoice has been printed or emailed, it can no longer be modified (as after printing or emailing, MIDAS assumes that the invoice has been "finalized"). Once an invoice has been "finalized", you can however still update its status as payments are received.
To update the status of an invoice:
Select the icon in the main toolbar.
On the invoicing screen, use the "Show Invoices" drop down to select "Invoices outstanding".
When the results are displayed, locate the invoice you wish to update the status of, and click/tap its corresponding icon.
The invoice will then be displayed along with a new editable field entitled "PAID".
Enter the amount the client has so far paid against this invoice into the PAID field, and select the "Update Status" button.