Shift Note- Attachment setup

Hello,

I'm trying to configure "Attachments" for shift notes.

When I go to "Shift Note Type" config screen> Press Attachment Check box> then try to select "Document Type" I am getting a error "No Values Found"

I already create a new document type in SPRO> CrossApplication> Document Management and created a new type, but I did not assign an object link because there is no option for "Shift Notes"

Is there any available documentation that will help configure the ability to create Attachment for shift notes or solution for my error.

Thanks,