We work with several agents in different countries for whom we need to track sales per customer and calculate commissions on paid invoices.

These sales agents are outside our organisation (taken as vendor contacts) and have no user account on our Odoo. I can't seem to be able to add their contact (vendor company) to the salesperson field for any specific customer of theirs. 

do I need to change something to the settings or do we need to get outside of standard for this? 

2) how can I set commission rules to be calculated on paid invoices and automatically accrued for in accounting app each quarter? ideally an invoice request is sent out with details of underlying paid invoices. 

Or version: Odoo 14 (on own server, not SH)

apps we have: contacts, sales, website, ecommerce, purchase inventory, manufacturing, accounting, email marketing.