This video explains how to validate closing and posting entries in POS on odoo 14 Community.
Odoo Point of Sale helps one to effectively track the cash flow happening within the sales counter during a session/shift. Once a product is purchased or billed in a POS session you need to validate it before closing the session. You should post the entries in Journal items before closing the session. In Odoo POS while you are closing the session a button is shown named ‘VALIDATE CLOSING & POSTING ENTRIES’ for this function. You need to click this button before closing the session & automatically post the entries into the journal.