与Laravel Echo和Pusher问题聊天应用程序

Question

I am learning to use Laravel Echo and Pusher and using this article as basis. I am getting this error:

Class 'Pusher' not found
in BroadcastManager.php (line 216)

I can see pusher in my vendor folder. I have followed instructions here and installed pusher already.

My .env file contains all required Pusher keys and config/broadcasting.php is set up pointing to .env.

What have I missed? Thanks.