Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Karl's link is 4 years old, but it does point you in the right general direction. You want to get the HUP discount. But I expect that you'll find that on the current version of the page MS has (dis)"improved" the offer to 30% off the price of Office 365 YEARLY subscriptions, ie "only" $60 per year instead of one3-time payment of $9-15 ... Hugely better for MS ...