title: Possible unhandled promise rejection (id 0) typeerror Body not allowed for GET or HEAD requests
body: <pre><code>import React from 'react';
  import { FlatList, ActivityIndicator, Text, View  } from 'react-native';
  
  export default class FetchExample extends React.Component {
  
    constructor(props){
      super(props);
      this.state ={ isLoading: true}
    }
  
    componentDidMount(){
  
          fetch('https://apitest.kuveytturk.com.tr/prep/v1/data/fecs', {
               method: 'GET',
               headers: {
                 Accept: 'application/json',
                 'Content-Type': 'application/json',
               },
               body: JSON.stringify({
                 firstParam: 'isoCode ',
                 secondParam: 'internationalCode',
                 thirdParam: 'name',
                 fourthParam: 'code',
                 FifthParam: 'group',
                 SixthParam: 'id'
               }),
             });
  
  }
  
  
    render(){
  
      if(this.state.isLoading){
        return(
          &lt;View style={{flex: 1, padding: 20}}&gt;
            &lt;ActivityIndicator/&gt;
          &lt;/View&gt;
        )
      }
  
      return(
        &lt;View style={{flex: 1, paddingTop:20}}&gt;
          &lt;FlatList
            data={this.state.dataSource}
            renderItem={({item}) =&gt; &lt;Text&gt;{item.isoCode}, {item.internationalCode}, {item.name}, {item.code}, {item.group}&lt;/Text&gt;}
            keyExtractor={({id}, index) =&gt; id}
          /&gt;
        &lt;/View&gt;
      );
    }
  }
  </code></pre>
  
  <p>I am the beginner of react native and i am trying to get data from api but i have an error about code.</p>
  
  <blockquote>
    <p>possible unhandled promise rejection (id 0) typeerror undefined is not an object</p>
  </blockquote>
  
  <p>I can't understand why there is no object</p>
  
  <p>Hope for your help.</p>