@Stella Sofia Isidro Sabate Welcome to Microsoft Q&A forums and thank you for your interest in Azure Cosmos DB.
With Azure Cosmos DB free tier, you'll get the first 1000 RU/s and 25 GB of storage in your account for free, applied at the account level.
Any RU/s and storage beyond 1000 RU/s and 25 GB will be billed at the regular pricing rates per the pricing page.
On the bill, you will not see a charge or line item for the free 1000 RU/s and 25 GB, only the RU/s and storage beyond what is covered by free tier.
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