Why our clients receiving "Only one entry is allowed" message?

We use jotform for our clients to register for programs. A few of our clients are receiving the message "sorry! only one entry is allowed". Could you explain this and how we can fix it?

The "unique submission" feature is enabled to your form that's why they are receiving that message.

To know more about unique submission, please check this guide: How-to-Set-Unique-Submissions-on-a-Form

To disable the unique submission, you need to set the "Check cookies only" to "No check".