Cant get Tax Override and new Disable Automatic Tax Calculation working with REST API and 23R1

We upgraded to 23R1 and our tax override code described in this old post stopped working.  

We also tried extending the web service endpoint and included the new field "DisableAutomaticTaxCalculation" in 23R1 and this did not help either.

Here is what the sample json: 

{
  "OrderType": {
    "value": "SO"
  },
  "CustomerID": {
    "value": "AMAZONG"
  },
  "Description": {
    "value": "Amazon Order"
  },
  "Details": [
    {
      "InventoryID": {
        "value": "ITEM1"
      },
      "OrderQty": {
        "value": 1.0
      },
      "UOM": {
        "value": "EA"
      },
      "UnitPrice": {
        "value": 9.99
      }
    }
  ],
  "TaxDetails": [
    {
      "TaxID": {
        "value": "MANUAL"
      },
      "TaxableAmount": {
        "value": 9.99
      },
      "TaxAmount": {
        "value": 1.00
      }
    }
  ],
  "TaxTotal": {
    "value": 1.00
  },
  "FinancialSettings": {
    "OverrideTaxZone": {
      "value": true
    },
    "CustomerTaxZone": {
      "value": "MANUAL"
    },
    "DisableAutomaticTaxCalculation": {
      "value": true
    }
  }
}

Also wondering why we don't have a new default endpoint for 23R1 to take advantage of the DisableAutomaticTaxCalculation new functionality out of the box instead of extending and maintaining custom end points.

Any ideas on what we are doing wrong to set the tax amounts manually?