Symptoms

You've added Attachment field to a Request Type, but customers don't see the field when creating a new request of that Request Type:

OR 

When trying to Edit fields for a Request Type you can not see Attachment listed:

When checking other Request types we can see Attachment field there. If trying to remove it you can not add it back.

Diagnosis

Check the followings from Project settings of the Service Management project:

1. From the Field Configuration used by the issue type associated with the request type, is Attachment visible or hidden? If hidden, Show it.
2. The field needs to be on the Create Issue Screen used by the issue type associated with the Request Type.
   1. Check under Project Settings > Screens - and make sure the field is not hidden
3. Make sure you have proper Permission set for Create Attachments
   1. Under Project Setting > Permissions
   2. If the permissions are set by roles, make sure your user has the roles assigned, under Project Settings > Users and roles
4. Do you see Attachment field on any other screen in Jira?
5. Is Attachments disabled in the System settings? It must be enabled from Jira Administration > System > Attachments for the field to be visible.