BTTC Promo 2 - D365 Finance additional base users on a monhtly basis

axperience_gra 

I think others already provided the answers to your situation, though not the answer you're looking for unfortunately.

BttC2 promo is only available in 3-year term. You can't do a month term with promo price. So that means you'll need to sell with default/full pricing when doing a month term. 

Each Base subscription for D365 F&O requires a 20-seat minimum, you can't purchase a new subscription for just 5 seats. You'll need to sell the minimum of 20 seats for a new month term subscription (even though you already reached that threshold in another subscription).  

While your situation makes perfect sense to do from a business point of view, unfortunately Microsoft is not able to support this case... 

If the customer only needs the 5 seats for a single month, then you it would make most sense to do 20 seats in month term for ~4K customer costs per month. 

If the customer expects to utilize these additional 5 seats multiple months within the 3-year term, then it might be more beneficial to purchase it in the existing BttC2 promo subscription. Think the break even point is around 4+ months.