For exemple, after sending a purchase order to one supplier, we receive a proforma invoice from them, to ask us to pay 50% of the amount. Where should we enter this proforma invoice in Odoo, and how should we specify the total amount and the 50%?

After the supplier has made the product, they send us another invoice, to ask us to pay the resting 50%. Where should we enter this invoice in Odoo, and how should we specify the total amount and the resting amount?

This is important for us to standardise our process, thank you for your help.