[The screenshots are of legacy webclient but it is same for UCI aka model driven app as well]
You can also refer to Image C attached
4. Now, most important step, have you provided appropriate permission to the webrole on notes entity?
For eg. If you want to enable attachment to the authenticated users, create an entity permission record, choose entity as notes, set the appropriate permissions here. That is referred in documentation above.
Do let me know if you have any more questions or does it solve the problem for you.