This article explains how the payment for your subscription is being re-calculated when you add/remove seats from your team.
Krisp subscriptions are prepaid and have specific next billing dates. Whenever you add a new seat to your team, the amount you pay for it is calculated based on the period left till the next billing date.
Let's look at an example with mock prices to make this clearer.
You have a monthly team subscription with 2 seats. Each seat costs $12 USD/month. You pay $24 USD at the beginning of the billing cycle. On the 10th day of the cycle, you decide to add 1 more seat. The full amount for it would have been $12 USD. However, you won't use that one seat for a whole month but for 20 days. So you will pay $12 USD/30 days * 20 days. That would make $8 USD. When the next billing cycle starts, you will pay the full amount for that seat along with your other seats. The payment will be done with a single invoice.
If you remove a seat at any time during the billing cycle, the seat count will be changed at that moment. However, the price re-calculation will be done for the next billing cycle.
This means that the removed seats are non-refundable. If you remove the seat by mistake and decide to add it back, you will be charged for it at that moment.