There are two fields that allow for numbers on properties of applications. Typically these fields are available to add the number of required recommenders and/or the number not required. These fields are grayed out and I do not know why.
Please be sure that the checkbox is marked when creating the application to Require Account Login for the grantee. Once that is marked (and should be by default once marked the first time) those fields will be made available on the Attachments.