Firebase Phone Auth - RecaptchaVerifier undefined

I'm trying to implement Firebase Phone Authentication in my Ember.js app but the function RecaptchaVerifier is not defined.

The packages I'm using are Ember Canary with Firebase 6.3.2 and Node 10.15.3. The problem is that when I try to run the function it is undefined. I already have initialized firebase and it is working great when I'm using authentication with email and password.

I followed the instructions from https://firebase.google.com/docs/auth/web/phone-auth?hl=es-419 and wrote this line window.recaptchaVerifier = new firebase.auth.RecaptchaVerifier('recaptcha-container'); to call the recaptcha. The method firebase.auth is defined and working correctly.

If anyone has an idea or another approach on how to implement this would be very helpful. Thanks in advance!