[keycloak-user] what does "unauthorized_client" mean?

[Tim Dudgeon]

I'm having problems generating an access token.

$ curl -X POST 
http://192.168.59.103:8080/auth/realms/Customer1/protocol/openid-connect/token 
-H "Content-Type: application/x-www-form-urlencoded" -d 'username=user2' 
-d 'password=user2' -d 'grant_type=password' -d 'client_id=app1'
{"error":"unauthorized_client"}

 From what I can see everything is set up correctly and looks the same 
to another realm/client/user that does work:
- realm exists and works
- user exists and can log in to console
- client has been created in realm

But I'm getting "unauthorized_client" error.
What should I look at?

Tim