Copying 7 column table to 6 column table

I'm porting SQL Server Integration Services packages to Azure Data Factory.

I have two tables (Table 1 and Table 2) which live on different servers. One has seven columns, the other six. I followed the example at https://docs.microsoft.com/en-us/azure/data-factory/data-factory-map-columns

Table 1 DDL:

CREATE TABLE dbo.Table1
(
    zonename nvarchar(max), 
    propertyname nvarchar(max), 
    basePropertyid int, 
    dfp_ad_unit_id bigint, 
    MomentType nvarchar(200), 
    OperatingSystemName nvarchar(50)
)

Table 2 DDL

CREATE TABLE dbo.Table2
(
    ZoneID int IDENTITY, 
    ZoneName nvarchar(max), 
    propertyName nvarchar(max), 
    BasePropertyID int, 
    dfp_ad_unit_id bigint, 
    MomentType nvarchar(200), 
    OperatingSystemName nvarchar(50)
)

In ADF, I define Table 1 as:

{
  "$schema": "http://datafactories.schema.management.azure.com/schemas/2015-09-01/Microsoft.DataFactory.Table.json",
  "name": "Table1",
  "properties": {
    "type": "AzureSqlTable",
    "linkedServiceName": "PlatformX",
    "structure": [
      { "name": "zonename" },
      { "name": "propertyname" },
      { "name": "basePropertyid" },
      { "name": "dfp_ad_unit_id" },
      { "name": "MomentType" },
      { "name": "OperatingSystemName" }
    ],
    "external": true,
    "typeProperties": {
      "tableName": "Platform.Zone"
    },
    "availability": {
      "frequency": "Day",
      "interval": 1
    }
  }
}

In ADF I define Table 2 as:

{
  "$schema": "http://datafactories.schema.management.azure.com/schemas/2015-09-01/Microsoft.DataFactory.Table.json",
  "name": "Table2",
  "properties": {
    "type": "SqlServerTable",
    "linkedServiceName": "BrixDW",
    "structure": [
      { "name": "ZoneID" },
      { "name": "ZoneName" },
      { "name": "propertyName" },
      { "name": "BasePropertyID" },
      { "name": "dfp_ad_unit_id" },
      { "name": "MomentType" },
      { "name": "OperatingSystemName" }
    ],
    "external": true,
    "typeProperties": {
      "tableName": "staging.DimZone"
    },
    "availability": {
      "frequency": "Day",
      "interval": 1
    }
  }
}

As you can see, Table2 has an identity column, which will automatically populated.

This should be a simple Copy activity:

{
  "$schema": "http://datafactories.schema.management.azure.com/schemas/2015-09-01/Microsoft.DataFactory.Pipeline.json",
  "name": "Copy_Table1_to_Table2",
  "properties": {
    "description": "Copy_Table1_to_Table2",
    "activities": [
      {
        "name": "Copy_Table1_to_Table2",
        "type": "Copy",
        "inputs": [
          { "name": "Table1" }
        ],
        "outputs": [
          {
            "name": "Table2"
          }
        ],
        "typeProperties": {
          "source": {
            "type": "SqlSource",
            "sqlReaderQuery": "select * from dbo.Table1"
          },
          "sink": {
            "type": "SqlSink"
          },
          "translator": {
            "type": "TabularTranslator",
            "columnMappings": "zonename: ZoneName, propertyname: propertyName, basePropertyid: BasePropertyID, dfp_ad_unit_id: dfp_ad_unit_id, MomentType: MomentType, OperatingSystemName: OperatingSystemName"
          }
        },
        "policy": {
          "concurrency": 1,
          "executionPriorityOrder": "OldestFirst",
          "retry": 3,
          "timeout": "01:00:00"
        },
        "scheduler": {
          "frequency": "Day",
          "interval": 1
        }
      }
    ],
    "start": "2017-07-23T00:00:00Z",
    "end": "2020-07-19T00:00:00Z"
  }
}

I figured by not mapping ZoneID, it would just be ignored. But ADF is giving me the following error.

Copy activity encountered a user error: GatewayNodeName=APP1250S,ErrorCode=UserErrorInvalidColumnMappingColumnCountMismatch,'Type=Microsoft.DataTransfer.Common.Shared.HybridDeliveryException,Message=Invalid column mapping provided to copy activity: 'zonename: ZoneName, propertyname: propertyName, basePropertyid: BasePropertyID, dfp_ad_unit_id: dfp_ad_unit_id, MomentType: MomentType, OperatingSystemName: OperatingSystemName', Detailed message: Different column count between target structure and column mapping. Target column count:7, Column mapping count:6. Check column mapping in table definition.,Source=Microsoft.DataTransfer.Common,'

In a nutshell I'm trying to copy a 7 column table to a 6 column table and Data Factory doesn't like it. How can I accomplish this task?