Flutter Registration with API

Try to below code help:

Create TextEditingController

  final TextEditingController email = new TextEditingController();
  final TextEditingController contact = new TextEditingController();
  final TextEditingController password = new TextEditingController();
  final TextEditingController conpassword = new TextEditingController();

Create one function for registration

register(String  email, contact, pass,conpass) async {
    Map data = {
      
      'Email': email,
      'Mobile': contact,
      'Password': pass,
      'RetypePassword': conpass,
    };
    print(data);

    String body = json.encode(data);
    var url="Your url here";
    var response = await http.post(
      url,
      body: body,
      headers: {
        "Content-Type": "application/json",
        "accept": "application/json",
        "Access-Control-Allow-Origin": "*"
      },
    );
    print(response.body);
    print(response.statusCode);
    if (response.statusCode == 200) {
      //Or put here your next screen using Navigator.push() method
      print('success');
    } else {
      print('error');
    }
  }

Create Button

ElevatedButton(
child:Text('Register'),
onPressed:(){
   register(email.text, contact.text, password.text, conpassword.text);
   },
),