Error trying to create a new container in existing container instance using yaml file

I'm trying to create a new container in an existing container instance (I assume you can have several containers in a container instance), but I get this error message:

(InvalidResourceLocation) The resource 'test-app' already exists in location 'australiasoutheast' in resource group 'algo_trading'. A resource with the same name cannot be created in location 'australiaeast'. Please select a new resource name.

Code: InvalidResourceLocation

Message: The resource 'test-app' already exists in location 'australiasoutheast' in resource group 'algo_trading'. A resource with the same name cannot be created in location 'australiaeast'. Please select a new resource name.

The image test-image exists in ACR, the existing container instance is called test-app.

This is the yaml file and I try to create the container using the command:

az container create --resource-group <resource_group> --file docker_compose_test_app.yaml

name: test-app # Name of the existing container group
apiVersion: '2021-10-01'
location: australiaeast
properties:
  containers:
  - name: test-cont  # name of the new container
    properties:
      image: test_image  # container image in acr used to create the instance
      resources:
        requests:
          cpu: 1
          memoryInGb: 1.5
      ports:
      - port: 5000
  osType: Linux
  ipAddress:
    type: Public
    ports:
    - protocol: tcp
      port: 5000
tags: {exampleTag: tutorial}