What is the proper image url to be entered in the yaml file for KNATIVE deployment

Question

I am trying to complete the KNative tutorial for deploying this tutorial : https://knative.dev/docs/serving/samples/hello-world/helloworld-ruby/

I have a url upon completion however, the page is not reachable. I am getting 404 not found.

When I run: kubectl get all , I get the following:

   NAME                                               CONFIG NAME     K8S SERVICE NAME      GENERATION   READY   REASON             ACTUAL REPLICAS   DESIRED REPLICAS
revision.serving.knative.dev/helloworld-go-00001   helloworld-go   helloworld-go-00001   1            True                       0                 0
revision.serving.knative.dev/sample-app-00001      sample-app                            1            False   ContainerMissing
revision.serving.knative.dev/sample-app-00002      sample-app                            2            False   ContainerMissing

Which leaves me to believe that there is something wrong with the image url specified in my yaml file. My yaml looks like this:

apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: sample-app
  namespace: default
spec:
  template:
    spec:
      containers:
        - image: docker.io/adet4ever/sample-app
          env:
            - name: TARGET
              value: "Ruby Sample v1"

I noticed that the only time a different app works is when I am ableto wget the image url like in the example here:https://docs.openshift.com/container-platform/4.1/serverless/getting-started-knative-services.html

I cannot wget this url and not sure why: docker.io/adet4ever/sample-app I created a docker hub account and pushed the image. I dont know if I am missing anything else. Thanks for helping as I have spent 2 days trying to fix this problem.