This issue can occur if the client you are billing does not have a default VAT code assigned to it.
You can find the default VAT code for a client by navigating to:
In DPS OneOffice/FD select File.
Select Clients.
Enter Client Ref, then click the Search spyglass.
Double click on Client.
Select Credit & Defaults tab.
Under Default codes, select a VAT Code from the dropdown selection.
Click Save.
This field auto-populates to VAT code 1 (standard rate 20%) when a user saves a client, unless they select an alternate VAT code. However an older version of Access Legal Case Management, stopped the auto-allocation of this field.
If you have many clients where the VAT code is missing, please raise a new case online and reference the title of this article, one of our support team agents can run a script on your database to auto-assign the VAT code for affected clients.