Reference type value changes to be array

[Productshothk]

I have tried the solution of How to insert reference type values to Firestore?
But the value is become array

Here is my code

    const data = {
      User: { $ref:"User/LjHVAMlm0yY3o5tktIkZ00aN0oC2" },
      }

  db.firestore().collection('Ticket').doc().set(data);