Firebase change password does not work. I get this error: The password is invalid or the user does not have a password

To change a user's password, it says to have them log in again to get fresh credentials. So I logged them in with this function:

Auth.auth().signIn(withEmail: enterEmailTextField.text!, password: enterOldPasswordLabel.text!) { [weak self] authResult, error in

But I get this error: The password is invalid or the user does not have a password.

Yet I can log out and sign back in on the login page and input the exact same input to the exact same function without issue. It makes no sense.

How do I gain a fresh login credential so they can change passwords? Because the method of logging them in again just does not work.

I also tried an alternate approach of using this function to get the credential:

let credential = EmailAuthProvider.credential(withEmail: enterEmailTextField.text!, password: enterOldPasswordLabel.text!)

I print the credential and it's not nil. I then plug it into this function and get the same error described above:

Auth.auth().currentUser?.reauthenticate(with: credential) { [weak self] _, error in
            if error != nil {
            print("error: \(error!)")
          } else {
...

How do you allow a user to change his or her Firebase password in Swift?