How do I disable daily automated backup for RDS?

I have setup an AWS Backup rule to backup a MariaDB instance:

• hourly At 50 minutes past the hour
• Start within 1 hour, complete within 2 hours
• Total retention period is 2 days
• continuous backup disabled But there are a few backup failed at the interval of 1:50, 2:50, 3:50 UTC:

When I clicked on the hyperlink of the job that failed, the error is: Invalid lifecycle: Backup job 6A26EC48-D3CC-7DB9-2E2B-E962B0863DCA could not start because it is either inside or too close to the automated backup window configured in RDS instance.

On RDS->Automated Backup, I can see that the rds is backuped every hour. But I have checked there is no automated turned on for that rds database instance (RDS->Database->Modify). How can I disable that automated backup?

Cheers