Hi @Seller_Zra00AeDwosci! We should have some resources to help here in addition to the response from Shahar above.

First, Seller University's Increase FBA capacity limits with Capacity Manager (3:38) which is a step by step walkthrough.

I also recommend reading through the Capacity Manager help page, where you'll see example tables of space and corresponding charges but also these important passages as they relate to your question:

The reservation fee is the amount per cubic foot of capacity requested that you would pay at the end of the specified period if your request is granted and you generate no sales during the period.

If your request is granted, we may reduce the reservation fee further at a later date in accordance with our lowest reservation fee guarantee. The fee can be partially or fully offset by the amount of performance credits that you earn.

Reservation fees are charged after the end of the specified period. For example, if you were granted additional capacity for October 1 through October 31, any reservation fees would be charged in early November.

and

What happens if my capacity limit increase request is granted?

When your request is granted, its status will change to granted in Capacity Manager, and you’ll be notified via email. Your new, higher limit will be used to determine how much inventory you can send to fulfillment centers and whether FBA inventory overage fees will be charged to your account.

No reservation fee charges will be applied to your account at the time your request is granted. At the end of the specified period, your account will be charged the difference, if any, between your total reservation fee and performance credits earned.

and

Will the reservation fee still be charged if I don’t use the additional capacity?

Yes. Your reservation fee isn’t affected by your actual use of the additional capacity granted.

If you aren’t confident that you can use the capacity efficiently and offset the reservation fee with performance credits, we recommend that you do not request the capacity, because you will be responsible for the remaining balance (your reservation fee minus performance credits). Your IPI score may also be affected if you request and receive additional capacity that you don’t use.

Hope these help!

Topher