How to send whatsapp messages via twilio and manage the replies via the mobile phone?

I would like to send a Whatsapp message via Twilio and be able manage the response via whatsapp mobile app. So i want the same account to be accessed via the api and the mobile App. Twilio gives me the error message below :

> "This number is registered to an existing WhatsApp account. To use
> this number, disconnect it from the existing account. Then, return to
> this page and re-enter the number. Note: It may take up to 3 minutes
> for the number to become available."

How can I accomplish this?

I use this code to send whatsapp message via Twilio :

  TwilioClient.Init(_Configs.Twilio.SID, _Configs.Twilio.Token);

                var message = MessageResource.Create(
                    body: whatsapp.Message,
                    from: new Twilio.Types.PhoneNumber("whatsapp:" + _Configs.Twilio.FromNumberWhatsapp), 
                    to: new Twilio.Types.PhoneNumber("whatsapp:+27" + whatsapp.CellNumber.Trim().Substring(1))
                );

Please recommend another service provider if it cant be done via Twilio.

The code you showed will send out a text message. If someone replies to that message, you'll receive a webhook request from Twilio. You'll need to set up a web application to handle that request.

Are you using .NET?
If so, you can:

1. Create an MVC project with ASP.NET
2. Install the Twilio.AspNet.Mvc package
3. Create a controller, i.e. SmsController.cs
4. Paste in the following code:

using Twilio.AspNet.Common;
using Twilio.AspNet.Mvc;
using Twilio.TwiML;

namespace WebApplication1.Controllers {
  public class SmsController: TwilioController {
    public TwiMLResult Index(SmsRequest incomingMessage) {
      var messagingResponse = new MessagingResponse();
      messagingResponse.Message("The copy cat says: " +
        incomingMessage.Body);

      return TwiML(messagingResponse);
    }

  }
}

5. Run the application
6. Host your app, you can use ngrok to test it out by creating a tunnel from the Internet to your localhost.
7. Copy the public URL and add it to your Twilio Console, and configure it when a Message comes in, it should hit this URL.

If you want more details, check out the documentation on how to Receive and Reply to Inbound SMS Messages with ASP.NET MVC.

This error message is correct. You cannot use a WA number on a mobile phone and on Twilio (or any other communications platform). If you want to use a mix of human-written and automated messages, you can build an application where a user can write the message that is then sent via the API.