An unexpected error occurred, please retry & Unable to fetch account usage data

The "Access denied" or "Unable to fetch account usage data" errors you're experiencing could be due to several reasons:

1. Insufficient permissions: Even if you have administrative access, billing and cost management features often require specific permissions. Your IAM user or role may not have the necessary permissions to access Cost Explorer or billing information.

2. Root user access requirement: Some billing and cost management features initially require root user access to enable IAM user access. You may need to log in as the root user to enable IAM access to billing information.

3. IAM access to billing not activated: The root account owner needs to explicitly activate IAM access to billing information in the account settings.

To resolve this issue, try these steps:

1. If you're using an IAM user, ensure the root user has activated IAM access to billing information:

• Sign in with root user credentials
• Navigate to Account settings
• Find "IAM User and Role Access to Billing Information"
• Enable this setting

2. Verify that your IAM user or role has the correct permissions for billing and Cost Explorer access.

3. Clear your browser cache and cookies, then:

• Sign out of the AWS Management Console
• Sign back in with your credentials
• Try to access the billing console again

4. If you're part of AWS Organizations, check if there are any Service Control Policies (SCPs) that might be restricting access.

5. Be aware that it can take up to 24 hours for cost and usage data to be prepared when you first access the Billing and Cost Management console.

If the issue persists after trying these steps, you may need to contact AWS Support for further assistance.
Sources
I get an error Access denied when I access New cost and usage report with date range of past 7 days, granularity daily, and group by dimension resource | AWS re:Post
Resolve access denied errors in the AWS Billing console | AWS re:Post

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