Determine via the AWS Console
If you're not sure if an account is the AWS payer, navigate to AWS Organizations in the AWS Console. If your screen looks similar to the below screenshot, the current account is the payer and will be flagged with a "star." Simply locate the corresponding account number as shown:
If you don't see this info, your account is a linked child account. To determine the payer account, navigate to the Billing Dashboard > Bills page and the payer account number will be in the upper right corner as shown:
Determine via the AWS CLI
Run the following AWS CLI command:
aws organizations describe-organization
Whether the current account is a payer or linked child account, the payer account number will be returned as MasterAccountId in the response.