How to access an image when setting up a container group via Azure CLI

I'm following this How-To guide:
https://learn.microsoft.com/en-us/azure/container-instances/container-instances-container-group-ssl

In the deploy-aci.yaml I need to replace the image with my own private image (stored in an Azure container registry). The example code is:

• name: my-app
  properties:
  image: mcr.microsoft.com/azuredocs/aci-helloworld

I tried this:

image: <mycontainerregistryname>.azurecr.io/<myrepositoryname>:<tag>

... and get an error:

The image '...' in container group '...' is not accessible. Please check the image and registry credential.

What is the correct syntax? Do I have to put in the password of the container registry?