Spill the Beans
means to accidentally or deliberately reveal a secret or disclose information that was meant to be kept confidential. It means to reveal a secret, whether it’s done by mistake or on purpose.
Examples:
1- An employee at the tech company spilled the beans about the features of the new smartphone before its official launch.
2- Sarah was planning a surprise party for her brother, but she accidentally spilled the beans when she mentioned it in front of him.