To add the attachment type value in web view:
  1. Navigate to Control Panel > Fields and Tables
  2. Go to the Tables tab
  3. Locate the Media Type table (for example, if you are trying to add an attachment type value for a deposit, you will locate the Treasury Media Type table)
  4. Click the ellipses next to it and select View
  5. Click the blue plus sign to add a new value
  6. Click Save
  7. Add the attachment in FE NXT again.

To add the attachment type value in database view:
  1. Switch to the Database View.
  2. Navigate to the appropriate module (General Ledger, Accounts Payable, etc)
  3. Select Configuration > Tables > Media Type
  4. Click "New Table Entry" to add a new Attachment type value.
  5. Click Save and Close
  6. Add the attachment in FE NXT again

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 and select Configuration > Tables > Treasury Media Type to add new type values.