in my app the user logged in using phone number auth from firebase , after logged he can add his email from profile fragment , i want to verify this email by sending email link from firebase but the problem always Failed to send the email, i dont know why

this is my code

btn.setOnClickListener {
            firebaseUser.sendEmailVerification()
                .addOnSuccessListener {
                    Toast.makeText(requireContext(), "is Success!!!", Toast.LENGTH_SHORT).show()
                }
                .addOnFailureListener {
                    Toast.makeText(requireContext(), "is Failure!!!", Toast.LENGTH_SHORT).show()
                }
        }

and i have enable email link and Email/Password auth in firebase , What could be the problem?