error message on subscription

Hello,
i have to say that this issue is not present on preprod platform (same as prod)

When a user try to subscribe (me with a test mail adress) a message “You do not have permission to add subscriber” is shown semms to not allow subscrption, but email suscriptions welcome are sent?
any solutionto avoid or fix this inelegant issue?

Thnks a lot for your urgent help

Laurent