These actions can only be performed with root AWS credentials
First login to the AWS console with the email/password credentials of the AWS root account. This can be done under https://console.aws.amazon.com/console/home.
Click on your account name on the top bar and go to My Security Credentials.
This can also be done directly on https://console.aws.amazon.com/iam/home?region=eu-west-1#/security_credentials.
Make sure to fill in your tax settings.
Do this by clicking on your account name on the top bar and go to My Billing Dashboard -> Tax settings.
This can also be done directly on https://console.aws.amazon.com/billing/home#/tax.
Make sure to have the complete tax information entered in Manage Tax Registration
In order to allow IAM users to access billing information IAM access to billing information must be activated.
Click on your account name on the top bar and go to My Account.
Scroll to IAM User and Role Access to Billing Information and activate IAM Access by editing this section.
Go to IAM or use the following URL https://console.aws.amazon.com/iam/home#/home.
Click on Customize at the IAM users sign-in link section.
Go to IAM -> Account settings or use the following URL https://console.aws.amazon.com/iam/home#/account_settings.
Configure the password policy to your needs.
Consider to use the following settings: