How to update payment method my root account?

Hi,

You might use a user with Administration permissions but not root (to sign-in as a root, you provide only email and password but not the account ID).

If you want to add permissions to manage billing with IAM Users please follow the documentation https://docs.aws.amazon.com/IAM/latest/UserGuide/tutorial_billing.html

If you're using root credentials, and not SSO or IAM roles/users then it looks like you are not logged into the Payer Management account of the organization. Normally, this issue happens if you are logged into the linked (member) account in the Organization. If that's the case, it's likely that there are SCPs (service control policies) set up on the Management Payer account that prevent linked accounts from accessing their billing pages. The payment method can only be updated on the Payer account as it pays the bill for the whole consolidated family.

However, if you are logged into the Management Payer account, you are probably logged into the account with the Administrator or Admin IAM role. By default, management of all the account management and billing related tasks is not enabled for IAM roles or users (By default, IAM users don't have access to the AWS Billing console). To enable it, you have to do it while logged in with root credentials (root email and password for the account) https://docs.aws.amazon.com/awsaccountbilling/latest/aboutv2/control-access-billing.html - after enabling it, you should be able to access billing page using Admin role.