For customers with multiple accounts we recommend AWS Organization's feature of Consolidated billing. You can read more about this feature here.
I would suggest opening a billing support case from your "main" account - which I assume is the Management Payer account of your Organization, so the support team could investigate your particular account setup, because there might be several reasons why this is happening. For example:
- In AWS Organizations, only the Payer account gets one consolidated invoice per month.
- However, linked accounts may be purchasing subscription services, for example Reserved Instances, Savings Plans, registering Route53 domains, buying products through AWS Marketplaces... In this case, a separate invoice will be created for each subscription (you can check with Support team if this can be consolidated)
- It's likely you didn't update tax / VAT settings on your accounts (you can update them from the Payer account on all your linked accounts in the tax settings page of the billing console), this might be impacting the amount of tax invoices you receive
I recommend contacting support (open a billing case) with this question to clarify what you can do. Most likely scenario (from my experience) - it's because of your tax settings.
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