Simple Client Example Fails with message required does not exist

[giesberge]

bridge_1 | 2021-07-21T16:55:37.540Z ros2-web-bridge:Bridge JSON command received: {"op":"call_service","id":"call_service:/add_two_ints:1","service":"/add_two_ints","type":"example_interfaces/AddTwoInts","args":{"a":1,"b":2}} bridge_1 | 2021-07-21T16:55:37.540Z ros2-web-bridge:Bridge Response: {"op":"status","level":"error","msg":"call_service: Error: The message required does not exist: example_interfaces, srv, AddTwoInts","id":"call_service:/add_two_ints:1"}

[sssxrf]

Same problem. Does anyone know how to solve that?