AWS Organization for billing purposes

Hello.

When an AWS account is invited to AWS Organizations, IAM roles etc. are automatically created, so I don't think there was anything that the user needed to create.
Additionally, once you accept the invitation, your managed account will automatically pay the bill.
https://docs.aws.amazon.com/organizations/latest/userguide/orgs_manage_accounts_invites.html

After an account accepts the invitation to join an organization, the management account of the organization becomes responsible for all charges accrued by the new member account. The payment method attached to the member account is no longer used. Instead, the payment method attached to the management account of the organization pays for all charges accrued by the member account.