Variables not being replaced in configuration at runtime

[ProNotion]

I have the following in my project file:

<Target Name="NSwag" AfterTargets="BeforeBuild" Condition=" '$(Configuration)' == 'Debug' ">
    <Exec WorkingDirectory="$(ProjectDir)" EnvironmentVariables="ASPNETCORE_ENVIRONMENT=Development" Command="$(NSwagExe) run nswag.config.nswag /variables:documentUrl=https://example.com/myapi.json" />
</Target>

Any my configuration file looks as follows:

{
  "runtime": "Default",
  "documentGenerator": {
    "fromDocument": {
      "url": "{documentUrl}",
      "output": null,
      "newLineBehavior": "Auto"
    }
  },
  "codeGenerators": {
    "openApiToCSharpClient": {
      "clientBaseClass": null,
      "configurationClass": null,
      "generateClientClasses": true,
      "suppressClientClassesOutput": false,
      "generateClientInterfaces": false,
      "suppressClientInterfacesOutput": false,
      "clientBaseInterface": null,
      "injectHttpClient": true,
      "disposeHttpClient": true,
      "protectedMethods": [],
      "generateExceptionClasses": true,
      "exceptionClass": "ApiException",
      "wrapDtoExceptions": true,
      "useHttpClientCreationMethod": false,
      "httpClientType": "RestSharp.RestClient",
      "useHttpRequestMessageCreationMethod": false,
      "useBaseUrl": true,
      "generateBaseUrlProperty": true,
      "generateSyncMethods": false,
      "generatePrepareRequestAndProcessResponseAsAsyncMethods": false,
      "exposeJsonSerializerSettings": false,
      "clientClassAccessModifier": "public",
      "typeAccessModifier": "public",
      "propertySetterAccessModifier": "",
      "generateNativeRecords": false,
      "generateContractsOutput": false,
      "contractsNamespace": null,
      "contractsOutputFilePath": null,
      "parameterDateTimeFormat": "s",
      "parameterDateFormat": "yyyy-MM-dd",
      "generateUpdateJsonSerializerSettingsMethod": true,
      "useRequestAndResponseSerializationSettings": false,
      "serializeTypeInformation": false,
      "queryNullValue": "",
      "className": "{controller}Client",
      "operationGenerationMode": "MultipleClientsFromOperationId",
      "additionalNamespaceUsages": [],
      "additionalContractNamespaceUsages": [],
      "generateOptionalParameters": false,
      "generateJsonMethods": false,
      "enforceFlagEnums": false,
      "parameterArrayType": "System.Collections.Generic.IEnumerable",
      "parameterDictionaryType": "System.Collections.Generic.IDictionary",
      "responseArrayType": "System.Collections.Generic.ICollection",
      "responseDictionaryType": "System.Collections.Generic.IDictionary",
      "wrapResponses": false,
      "wrapResponseMethods": [],
      "generateResponseClasses": true,
      "responseClass": "SwaggerResponse",
      "namespace": "My.Api",
      "requiredPropertiesMustBeDefined": true,
      "dateType": "System.DateTimeOffset",
      "jsonConverters": null,
      "anyType": "object",
      "dateTimeType": "System.DateTimeOffset",
      "timeType": "System.TimeSpan",
      "timeSpanType": "System.TimeSpan",
      "arrayType": "System.Collections.Generic.ICollection",
      "arrayInstanceType": "System.Collections.ObjectModel.Collection",
      "dictionaryType": "System.Collections.Generic.IDictionary",
      "dictionaryInstanceType": "System.Collections.Generic.Dictionary",
      "arrayBaseType": "System.Collections.ObjectModel.Collection",
      "dictionaryBaseType": "System.Collections.Generic.Dictionary",
      "classStyle": "Poco",
      "jsonLibrary": "SystemTextJson",
      "generateDefaultValues": true,
      "generateDataAnnotations": true,
      "excludedTypeNames": [],
      "excludedParameterNames": [],
      "handleReferences": false,
      "generateImmutableArrayProperties": false,
      "generateImmutableDictionaryProperties": false,
      "jsonSerializerSettingsTransformationMethod": null,
      "inlineNamedArrays": false,
      "inlineNamedDictionaries": false,
      "inlineNamedTuples": true,
      "inlineNamedAny": false,
      "generateDtoTypes": true,
      "generateOptionalPropertiesAsNullable": false,
      "generateNullableReferenceTypes": false,
      "templateDirectory": null,
      "serviceHost": null,
      "serviceSchemes": null,
      "output": "Clients/{controller}Client",
      "newLineBehavior": "Auto"
    }
  }
}

My documentUrl placeholder is never replaced with the variable. nswag is aware of my variable as I can see in my console:

Executing file 'nswag.config.nswag' with variables 'documentUrl=https://example.com/myapi.json'...
System.IO.FileNotFoundException: Could not find file 'D:\Repositories\MyPath\MyApi{documentUrl}'.
File name: 'D:\Repositories\MyPath\MyApi{documentUrl}'

So why is it not being replaced? If I use environment variables it works but even if I try and run this directly in a terminal it does not get replaced:

nswag run .\nswag.config.nswag /variables:documentUrl=https://example.com/myapi.json

Can anyone please advise what I am doing wrong?

The target framework for my project is net7.0.