使用AWS STS时，哪个AWS账户需要付费？

Question

我希望使用AWS STS从另一个团队拥有的另一个AWS账户访问资源。

说，AWS账户A试图访问AWS账户B.

basically the steps I am following:
1. Create a user in Account A
2. Create Role in Account B with the necesaary permissions
3. Add assume role permissions for user in Account A
4. Use User credentials to get temporary credentials for Account B.
5. Use temp credentials on Account B.

但是，在阅读了大量AWS文档之后，我无法确定哪个帐户需要为跨帐户API调用付费？