Answer

To use properties across different stacks, you need to explicitly export the values on the one end and import into the other stack.

In your case you would propably need something like this:

Stack: sns-test

{
    "Resources": {
        "MySNSTopic": {
            "Type": "AWS::SNS::Topic"
        }
    },
    "Outputs": {
        "MySNSTopicOutput": {
            "Description": "SNS topic arn",
            "Value": {
                "Ref": "MySNSTopic"
            },
            "Export": {
                "Name": {
                    "Fn::Sub": "${AWS::StackName}-MySNSTopicExport"
                }
            }
        }
    }
}

Stack: sns-subscription

{
  "Resources": {
    "MySubscription": {
      "Type": "AWS::SNS::Subscription",
      "Properties": {
        "Endpoint": "jens@apimeister.com",
        "Protocol": "email",
        "TopicArn": {
          "Fn::ImportValue" : "sns-test-MySNSTopicExport"
        }
      }
    }
  }
}

Source: https://stackoverflow.com/questions/47917472/cloudformation-sns-template-validation-error
Author: jens walter

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