I'm trying to connect Watson with Google Assistant, but I'm receiving a warning in firebase "Billing account not configured. External network is not accessible and quotas are severely limited. Configure billing account to remove these restrictions".
As noted in the Firebase pricing guide, for the free "Spark Plan", Firebase Functions can only connect to other Google services, not outbound connections such as IBM's Watson.
To remedy this, the easiest solution would be to configure a billing account and upgrade to the "Blaze Plan", where you can pay as you go. This allows your project to scale effectively, while primarily remaining free. However, in the event that you manage to exceed the quota, there will be some billing set up to charge you instead of failing.