bing-ads-mcp: Cannot create Shopping campaigns via mutate

[ctrlswing]

Summary

The mutate tool cannot create Shopping campaigns. Campaign creation works for Search campaigns, but fails with "The request message is null" when CampaignType: "Shopping" and ShoppingSetting are included.

Steps to Reproduce

{
  "entity": "campaigns",
  "create": {
    "Name": "1011 - US - Barks No More - Shopping",
    "BudgetType": "DailyBudgetStandard",
    "DailyBudget": 30,
    "CampaignType": "Shopping",
    "Settings": [{
      "Type": "ShoppingSetting",
      "StoreId": 3510637,
      "Priority": 0,
      "SalesCountryCode": "US"
    }],
    "BiddingScheme": { "Type": "EnhancedCpcBiddingScheme" },
    "Status": "Paused"
  }
}

Error: Bing Ads API request failed (400): The request message is null.

Also fails without the Settings block — just having CampaignType: "Shopping" triggers the error.

Expected Behavior

Should create a Shopping campaign linked to the specified Merchant Center store, same as creating one through Bing Ads Editor or the UI.

Context

• Package: @channel47/bing-ads-mcp@^1.1.3
• Basic Search campaign creation works fine (tested and confirmed)
• Dry run validation passes — the failure is at the Bing Ads API serialization level
• This blocks programmatic Shopping campaign setup across accounts that have healthy product feeds but no campaigns yet

Workaround

Currently creating Shopping campaigns manually via Bing Ads UI/Editor.