When the vendor workflow is used, changes that are made to specific fields are sent to the workflow for approval before they are added to the vendor, including the terms of payment field. This feature works only for editing vendors. If the fields like terms of, payment schedule are enabled for vendor approval, they will get the default value from vendor group only for editing the vendor. If the user is creating a new vendor and the fields are enabled for vendor approval, they will not get default value from vendor group or payment terms. Customer needs to set these values manually.
Please release a new feature vendor approval workflow for newly created vendors.