Получение строки React Native

<?php
include("Config.php");

$username = $_POST['username'];
$password = $_POST['password'];
$link = mysqli_connect("$HostName", "$HostUser", "$HostPass", "$DatabaseName");
if (!$link) {
die('Could not connect: ' . mysql_error());
}
$check = mysqli_query($link,"SELECT mail FROM Usuarios WHERE `mail`= '$username' AND `contraseña`= '$password'");
$numrows = mysqli_num_rows($check);
				if ($numrows == 0 )
				{
					//WRONG PASSWORD
					die("Wrong Password");
				}
else {
					//login user
					$row = mysqli_fetch_array($check);
					$mail = $row['mail'];
					$array = array('mail' => $mail); 
					$answer = json_encode($array);//"Login Done," . $mail;
					echo($answer);
}
mysqli_close($link);
?><?php
function safe($variable)
{
    $variable = addslashes(trim($variable));
    return $variable;
}
?>

import React from 'react';
import { StyleSheet, TouchableOpacity, TextInput, Text, View, Alert } from 'react-native';
import styles from './From.styles.js'


export default class Form extends React.Component
{

constructor(props) {

  super(props)

  this.state = {
    UserEmail: '',
    UserPassword: ''
}
  }

UserLoginFunction = () =>{

 const { UserEmail }  = this.state ;
 const { UserPassword }  = this.state ;


fetch('https://andrianodna.000webhostapp.com/Login.php', {
  method: 'POST',
  headers: {
    'Accept': 'application/json',
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
   username: UserEmail,
   password: UserPassword
  })

})
      .then((response) => response.text())

      .then((responseJson) => {

       if (responseJson === 'Wrong Password')
        {
              //Alert.alert(responseJson);
              Alert.alert('E-Mail o Contraseña equivocados')
            //Then open Profile activity and send user email to profile activity.
        }
        else{
          this.props.navigation.navigate('Router', { Email: UserEmail });
          //Alert.alert(responseJson);
        }

      }).catch((error) => {
        console.error(error);
      });


  }
  render()
  {
    return (

      <View style = {styles.container}>
            <TextInput style  = {styles.input}
            placeholder = 'E-Mail'
            onChangeText = {UserEmail => this.setState({UserEmail})}
            placeholderTextColor = "rgba(0,0,0,0.3)"
            keyboardType = "email-address"
            underlineColorAndroid='rgba(0,0,0,0)'/>

            <TextInput style  = {styles.input}
            placeholder = 'Contraseña'
            onChangeText = {UserPassword => this.setState({UserPassword})}
            placeholderTextColor = "rgba(0,0,0,0.3)"
            underlineColorAndroid='rgba(0,0,0,0)'
            secureTextEntry = {true} />

            <TouchableOpacity onPress = {this.UserLoginFunction} style = {styles.Button}>
             <Text style = {styles.buttonText}>{this.props.type}</Text>
           </TouchableOpacity>
           <TouchableOpacity style = {styles.Button2}>
            <Text style = {styles.buttonText}>{this.props.type2}</Text>
          </TouchableOpacity>


          </View>
      );
  }
}