Pipeline script failing because of creds not found

I've followed each step in the example and i've understood the concept. (Atleast thats what I think)
Now, when I edit the **Jenkinsfile_container_plugin** and supply the ID of my credentials, it's saying creds not found. Any idea why this is not working?

gist: https://gist.github.com/vighneshpai-yml/56ab10de14f29416b9fdbbde0faa8c18