Custom form - Duplicate Value Present

I am new to Zoho People. I create a new form on Zoho People quite simple.

A date (by default the current date) and a radio button with 3 options (Yes, No, Not applicable)

I defined the date as ‘No duplicate’ as only one entry by date is allowed.

I added:

- one record on Feb 1 with the value Yes

- one record on Feb 2 with the value No

- one record on Feb 3 with the value Not Applicable

When entering the record for Feb 4 with the value Yes, I get Duplicate value present on the radio button.

Removing the ticked box on the date on ‘No Duplicate’ does not help.

Any suggestions are welcome.

Thank you