Looking for a Regex for only a certain type of chars and no duplication

Question

I am looking for a regex only for certain chars and no duplications. I have to write an app for a restaurant and they want to write the allergens of the food (ABCDEFGHLMNOPR). Therefore only those chars should be allowed without duplications.

I am using primefaces and I tried a lot of different regex before. They worked on https://regex101.com/r/dVohnx/1 but sadly not in the app.

//this regEx works on regex101 online editor but not for me.

<p:inputText id="id" value="#{allergene}" disabled="#{!speiseplanView.editable and hasEditPermission}">
   <p:keyFilter regEx="/^(?:([ABCDEFGHLMNOPR])(?!\1))+$/" />
</p:inputText>

The problem is, I only limited the chars with that code but not the duplication.

thank you, guys!