java - Android index php file does not register the user -

i'm following this tutorial android hive on how create login , registration system using php , mysql; however, i'm having difficulties registering user.

edit: problem whenever register button clicked returns "required tag missing" , not store data should.

i have tried using advanced rest client extension google chrome, didn't provide me useful information.

the index.php file contains functions storing , getting data of users database:

<?php //this file has role fo accepting requests , giving json responses. // accepts post , requests   if (isset($_post['tag']) && $_post['tag'] != ''){     //get tag     $tag = $_post['tag'];      //include database handler     require_once 'login_api/db_functions.php';     $db = new db_functions();      //reponse array     $response = array("tag" => $tag, "error" => false);      //check tag type     if ($tag == 'login'){         //request type going to check login         $email = $_post['email'];         $password = $_post['password'];          //check user         $user = $db->getusersbyemailandpassword($email, $password);         if ($user != false){             //this mean user has been found             $response["error"] = false;             $response["uid"] = $user["unique_id"];             $response["user"]["name"] = $user["name"];             $response["user"]["email"] = $user["email"];             $response["user"]["created"] = $user["created"];             $response["user"]["updated"] = $user["updated"];             echo json_encode($response);         }else {             //user not found             //echo json error = 1             $response["error"] = true;             $response["error_msg"] = "incorrect email or password";             echo json_response($response);         }     }else if ($tag == 'register') {         //request type register new user         $name = $_post['name'];         $email = $_post['email'];         $password = $_post['password'];          //check see if user exists         if ($db->isuserexisted($email)){             //user exists produce error response             $response["error"] = true;             $response["error_msg"] = "user exists";             echo json_encode($response);         }else{             //store user             $user = $db->storeuser($name, $email, $password);             if ($user){                 //user stored                 //creating data json                 $response["error"] = false;                 $response["uid"] = $user["unique_id"];                 $response["user"]["name"] = $user["name"];                 $response["user"]["email"] = $user["email"];                 $response["user"]["created"] = $user["created"];                 $response["user"]["updated"] = $user["updated"];                 echo json_encode($response);             }else{                 //failure storing user details database                 $response["error"] = true;                 $response["error_msg"] = "an error has occured registering..";                 echo json_encode($response);             }         }         }else {         //user failed store         $response["error"] = true;         $response["error_msg"] = "uknown 'tag', should either login or  register";         echo json_encode($response);         }     }else {     $response["error"] = true;     $response["error_msg"] = "required, 'tag' missing";     echo json_encode($response);     }  ?> 

my registeractivity:

public void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_register);      inputfullname = (edittext) findviewbyid(r.id.name);     inputemail = (edittext) findviewbyid(r.id.email);     inputpassword = (edittext) findviewbyid(r.id.password);     btnregister = (button) findviewbyid(r.id.btnregister);     btnlinktologin = (button) findviewbyid(r.id.btnlinktologinscreen);      // progress dialog     pdialog = new progressdialog(this);     pdialog.setcancelable(false);      // session manager     session = new sessionmanager(getapplicationcontext());      // sqlite database handler     db = new sqlitehandler(getapplicationcontext());      // check if user logged in or not     if (session.isloggedin()) {         // user logged in. take him main activity         intent intent = new intent(registeractivity.this,                 mainactivity.class);         startactivity(intent);         finish();     }      // register button click event     btnregister.setonclicklistener(new view.onclicklistener() {         public void onclick(view view) {             string name = inputfullname.gettext().tostring();             string email = inputemail.gettext().tostring();             string password = inputpassword.gettext().tostring();              if (!name.isempty() && !email.isempty() && !password.isempty()) {                 registeruser(name, email, password);             } else {                 toast.maketext(getapplicationcontext(),                         "please enter details!", toast.length_long)                         .show();             }         }     });      // link login screen     btnlinktologin.setonclicklistener(new view.onclicklistener() {          public void onclick(view view) {             intent = new intent(getapplicationcontext(),                     loginactivity.class);             startactivity(i);             finish();         }     });  }  /**  * function store user in mysql database post params(tag, name,  */ private void registeruser(final string name, final string email,                           final string password) {     // tag used cancel request     string tag_string_req = "req_register";      pdialog.setmessage("registering ...");     showdialog();      stringrequest strreq = new stringrequest(method.post,             appconfig.url_register, new response.listener<string>() {          @override         public void onresponse(string response) {             log.d(tag, "register response: " + response.tostring());             hidedialog();              try {                 jsonobject jobj = new jsonobject(response);                 boolean error = jobj.getboolean("error");                 if (!error) {                     // user stored in mysql                     // store user in sqlite                     string uid = jobj.getstring("uid");                      jsonobject user = jobj.getjsonobject("user");                     string name = user.getstring("name");                     string email = user.getstring("email");                     string created = user                             .getstring("created");                      // inserting row in users table                     db.adduser(name, email, uid, created);                      // launch login activity                     intent intent = new intent(                             registeractivity.this,                             loginactivity.class);                     startactivity(intent);                     finish();                 } else {                      // error occurred in registration. error                     // message                     string errormsg = jobj.getstring("error_msg");                     toast.maketext(getapplicationcontext(),                             errormsg, toast.length_long).show();                 }             } catch (jsonexception e) {                 e.printstacktrace();             }          }     }, new response.errorlistener() {          @override         public void onerrorresponse(volleyerror error) {             log.e(tag, "registration error: " + error.getmessage());             toast.maketext(getapplicationcontext(),                     error.getmessage(), toast.length_long).show();             hidedialog();         }     }) {          @override         protected map<string, string> getparams() {             // posting params register url             map<string, string> params = new hashmap<string, string>();             params.put("tag", "register");             params.put("name", name);             params.put("email", email);             params.put("password", password);              return params;         }      };      // adding request request queue     appcontroller.getinstance().addtorequestqueue(strreq, tag_string_req); }  private void showdialog() {     if (!pdialog.isshowing())         pdialog.show(); }  private void hidedialog() {     if (pdialog.isshowing())         pdialog.dismiss(); } }