- Switch to the Database View.
- Navigate to the appropriate module (General Ledger, Accounts Payable, etc)
- Select Configuration > Tables > Media Type
- Click "New Table Entry" to add a new Attachment type value.
- Save and Close.
- Add the attachment in FENXT.
Note: if you're trying to add an attachment to a deposit from the Treasury menu, you'll want to make sure you go to the appropriate module select Configuration > Tables > Treasury Media Type to add new type values.