'AWS: Budget's alert triggered but no cost related

I have a RDS database (cheapest one) : T3.micro, gp2, 20GiB, no storage autoscaling with a beanstalk environment.

For 3 days I received a budget's alert (you can find the budget history graph below):

When I go in AWS Cost explorer to have more details daily cost is stuck at 0:

Do you know why cost is not up to date, and how I can investigate on it?

Thanks.

Solution 1:^[1]

In cost explorer the white bars are forecasts (also see https://aws.amazon.com/blogs/aws-cloud-financial-management/launch-usage-based-forecasting-now-available-in-aws-cost-explorer/). Because it is a forecast for the future no money was payed yet and therefore costs (purple bar) are 0.

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Solution	Source
Solution 1	Martin Garbe