Стойността на свойството VPCZoneIdentifier трябва да бъде от тип List of String

"wordpressASG": {
      "Type": "AWS::AutoScaling::AutoScalingGroup",
      "Properties": {
        "AvailabilityZones": [
          "ap-southeast-2a",
          "ap-southeast-2b"
        ],
        "VPCZoneIdentifier": [
          {
            "ref": "subnetA"
          },
          {
            "ref": "subnetB"
          }
        ],
        "MinSize": "0",
        "HealthCheckGracePeriod": 300,
        "MaxSize": "0",
        "Cooldown": "300",
        "LaunchTemplate": {
          "LaunchTemplateId": {
            "Ref": "wordpressTemplate"
          },
          "Version": {
            "Fn::GetAtt": [
              "wordpressTemplate",
              "LatestVersionNumber"
            ]
          }
        },
        "MetricsCollection": [
          {
            "Granularity": "1Minute",
            "Metrics": [
              "GroupMinSize",
              "GroupMaxSize"
            ]
          }
        ],
        "TargetGroupARNs": [
          {
            "Ref": "wordpressTG"
          }
        ]
      }
    }