What did Kris and Fred tell Doris her problem was in a Miracle on 34th Street?

In "Miracle on 34th Street," Kris Kringle, not Fred, tells Doris that her problem is she has lost her belief in the magic of Christmas.

Here's the exchange:

Kris: "You don't believe, do you?"

Doris: "Believe what?"

Kris: "In me. In Santa Claus. In Christmas."

Doris: "Well, I'm a grown-up."

Kris: "You're a grown-up, but you're not too old to believe in something. You've got to believe in something, Doris. You've got to believe in something."

This moment is pivotal in the film, as it shows how Doris's cynicism and skepticism have affected her life. Kris encourages her to rediscover the joy and wonder of Christmas, which ultimately helps her to reconnect with her inner child and find happiness.