In OneOfficeERP POS module, the invoices are auto generated. You can set your complete POS system right with the following configuration steps:
Create a Loyalty program in the doctype: You can set Single Tier or a Multiple Tier Program based on the slabs existing in the amount of Purchase that is done in OneOfficeERP.
Once the loyalty program is set, you can create a Customer and link the Loyalty program to it.
Once this Customer is linked to the Loyalty program, you can now setup your POS profile if it is not set yet: