How can i give accessibilityIdentifier to text field, because if i add accessibilityIdentifier to FloatingLabelTextField it did not work with UI Test Case

Example:

FloatingLabelTextField($firstName, placeholder: "First Name", editingChanged: { (isChanged) in 
})
accessibilityIdentifier("firstname_textfield")

Than i code in Test Case

let firstnameTextField = app.textFields["firstname_textfield"]
        firstnameTextField.tap()
        firstnameTextField.typeText("test user")

in text field it is not typing "test user"
can you please let me know how to make working in UI Test Case?