How to Give Permission on POS Session
When you’ve enabled POS session, all users can open and close session. However, you can set up additional permissions if necessary.
Goto Magento Backend > POS > Manage Roles
Create a new role or edit an existing role by In Permission tab, under Role Resources > Resource Access: Select Custom
Go to Magento Backend > POS > Manage Staffs:
Select a staff and go to POS permission
Assign the correct Role for that staff and save your settings.