Level=error msg="opentracing: Invalid Inject/Extract carrier" when using zipkin

I enabled tracing and I am just checking the error logs of Traefik and I am seeing the following message for every request:

level=error msg="opentracing: Invalid Inject/Extract carrier"

Here's my setup:

  - --tracing.zipkin.httpEndpoint=http://zipkin:9411/api/v2/spans
  - --tracing.zipkin.samespan=true

And I happen to have this service

  zipkin:
    image: openzipkin/zipkin
    networks:
      - internal
    deploy:
      resources:
        limits:
          cpus: '0.5'
          memory: 128M