Exact match in string array

Hello, I would like to create a simple function which will be able to verify in an array of string the exact correspondence of the value entered by the user.

Here is an example, however it returns true as soon as a letter matches the string

IF(IN(fieldname2, ["Ramecourt", "Saint-Pol"]), "ZONE 1", "ZONE INCONNUE")

–> If user type : “R” it returns true = “ZONE 1”
–> User needs to type “Ramecourt” or “Saint-Pol” or “ramecourt” for a valid return…

Can you help me people?
Thanks a lot