Ionic 4 native http POST with multiple headers - cordova-plugins

Question

Here is how I am doing an http post from my Ionic app:
import { HTTP } from '#ionic-native/http/ngx';
someAction(assetId: number, userId: number)
{
var asset: Asset = new Asset();
asset.assetId = assetId.toString();
asset.userId = userId.toString();
const options = {
headers: "Content-Type: application/json; charset=utf-8"
};
return this.http.post(this.url + "someAction", asset, options).then(data => {
return "Done";
}).catch(err => {
console.log(err);
});
}
According to the documentation here - https://www.npmjs.com/package/cordova-plugin-advanced-http#post, the headers should be sent like so:
headers: { 'content-length': '247' }
Which is not working for me. Note how I am sending the header key and value as one string:
headers: "Content-Type: application/json; charset=utf-8"
This is the error -
Error: advanced-http: header values must be strings
at checkKeyValuePairObject (helpers.js:88)
at checkHeadersObject (helpers.js:192)
at Object.handleMissingOptions (helpers.js:309)
at Object.sendRequest (public-interface.js:143)
at Object.post (public-interface.js:167)
at callCordovaPlugin (vendor.js:76774)
at vendor.js:76589
at vendor.js:76547
at new ZoneAwarePromise (polyfills.js:3268)
at tryNativePromise (vendor.js:76546)
I get the same error when trying to send multiple headers. I am at a loss as to why this is happening - the example in the documentation does not work! What am I missing?
Edit: web.config
<?xml version="1.0" encoding="utf-8"?>
<configuration>
<configSections>
<section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler, log4net" />
</configSections>
<connectionStrings>
<add name="Default" connectionString="..." />
</connectionStrings>
<appSettings>
...
</appSettings>
<system.web>
<compilation debug="true" targetFramework="4.5.2" />
<httpRuntime targetFramework="4.5.2" maxRequestLength="75096" executionTimeout="600" />
</system.web>
<runtime>
<assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
<dependentAssembly>
<assemblyIdentity name="Microsoft.Owin" publicKeyToken="31bf3856ad364e35" culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-4.0.0.0" newVersion="4.0.0.0" />
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="System.IdentityModel.Tokens.Jwt" publicKeyToken="31bf3856ad364e35" culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-5.2.2.0" newVersion="5.2.2.0" />
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="Microsoft.IdentityModel.Protocol.Extensions" publicKeyToken="31bf3856ad364e35" culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-1.0.40306.1554" newVersion="1.0.40306.1554" />
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="Microsoft.Owin.Security" publicKeyToken="31bf3856ad364e35" culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-3.1.0.0" newVersion="3.1.0.0" />
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="Microsoft.Owin.Security.OAuth" publicKeyToken="31bf3856ad364e35" culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-3.1.0.0" newVersion="3.1.0.0" />
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="Microsoft.Owin.Security.Jwt" publicKeyToken="31bf3856ad364e35" culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-3.1.0.0" newVersion="3.1.0.0" />
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="Microsoft.IdentityModel.Tokens" publicKeyToken="31bf3856ad364e35" culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-5.2.2.0" newVersion="5.2.2.0" />
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="System.Web.Http" publicKeyToken="31bf3856ad364e35" culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-5.2.6.0" newVersion="5.2.6.0" />
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="System.Net.Http.Formatting" publicKeyToken="31bf3856ad364e35" culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-5.2.6.0" newVersion="5.2.6.0" />
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="Autofac" publicKeyToken="17863af14b0044da" culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-4.8.1.0" newVersion="4.8.1.0" />
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="System.Web.Http.WebHost" publicKeyToken="31bf3856ad364e35" culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-5.2.6.0" newVersion="5.2.6.0" />
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="System.Web.Mvc" publicKeyToken="31bf3856ad364e35" culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-5.1.0.0" newVersion="5.1.0.0" />
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="Newtonsoft.Json" publicKeyToken="30ad4fe6b2a6aeed" culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-11.0.0.0" newVersion="11.0.0.0" />
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="System.Web.WebPages" publicKeyToken="31bf3856ad364e35" culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-3.0.0.0" newVersion="3.0.0.0" />
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="System.Web.Razor" publicKeyToken="31bf3856ad364e35" culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-3.0.0.0" newVersion="3.0.0.0" />
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="System.Web.WebPages.Razor" publicKeyToken="31bf3856ad364e35" culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-3.0.0.0" newVersion="3.0.0.0" />
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="WebGrease" publicKeyToken="31bf3856ad364e35" culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-1.5.2.14234" newVersion="1.5.2.14234" />
</dependentAssembly>
</assemblyBinding>
</runtime>
<system.codedom>
<compilers>
<compiler language="c#;cs;csharp" extension=".cs" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.CSharpCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" warningLevel="4" compilerOptions="/langversion:6 /nowarn:1659;1699;1701" />
<compiler language="vb;vbs;visualbasic;vbscript" extension=".vb" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.VBCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" warningLevel="4" compilerOptions="/langversion:14 /nowarn:41008 /define:_MYTYPE=\"Web\" /optionInfer+" />
</compilers>
</system.codedom>
<system.webServer>
<validation validateIntegratedModeConfiguration="false" />
<modules runAllManagedModulesForAllRequests="true">
<remove name="FormsAuthentication" />
<remove name="WebDAVModule" />
</modules>
<handlers>
<remove name="WebDAV" />
<remove name="ExtensionlessUrlHandler-ISAPI-4.0_32bit" />
<remove name="ExtensionlessUrlHandler-ISAPI-4.0_64bit" />
<remove name="ExtensionlessUrlHandler-Integrated-4.0" />
<add name="ExtensionlessUrlHandler-ISAPI-4.0_32bit" path="*." verb="GET,HEAD,POST,DEBUG,PUT,DELETE,PATCH,OPTIONS" modules="IsapiModule" scriptProcessor="%windir%\Microsoft.NET\Framework\v4.0.30319\aspnet_isapi.dll" preCondition="classicMode,runtimeVersionv4.0,bitness32" responseBufferLimit="0" />
<add name="ExtensionlessUrlHandler-ISAPI-4.0_64bit" path="*." verb="GET,HEAD,POST,DEBUG,PUT,DELETE,PATCH,OPTIONS" modules="IsapiModule" scriptProcessor="%windir%\Microsoft.NET\Framework64\v4.0.30319\aspnet_isapi.dll" preCondition="classicMode,runtimeVersionv4.0,bitness64" responseBufferLimit="0" />
<add name="ExtensionlessUrlHandler-Integrated-4.0" path="*." verb="GET,HEAD,POST,DEBUG,PUT,DELETE,PATCH,OPTIONS" type="System.Web.Handlers.TransferRequestHandler" preCondition="integratedMode,runtimeVersionv4.0" />
</handlers>
<security>
<requestFiltering>
<verbs allowUnlisted="false">
<clear />
<add verb="GET" allowed="true" />
<add verb="POST" allowed="true" />
<add verb="DELETE" allowed="true" />
<add verb="PUT" allowed="true" />
<add verb="OPTIONS" allowed="true" />
</verbs>
</requestFiltering>
</security>
<httpProtocol>
<customHeaders>
<add name="Access-Control-Allow-Origin" value="*" />
</customHeaders>
</httpProtocol>
</system.webServer>
<log4net>
...
</log4net>
</configuration>

Answer 1

Your headers should be an object:
const options = {
headers: {
'Content-Type': 'application/json'
}
};
Also, most likely you will need to enable CORS headers. Depending on your Web API version you can try one of this: Enabling CORS with WebAPI PUT / POST requests? or https://learn.microsoft.com/en-us/aspnet/web-api/overview/security/enabling-cross-origin-requests-in-web-api