React axios Post error, data format error

Is because with Axios you are sending the data in JSON format and with fetch is sent in Form Data format, to send it with Axios in Form Data format you need to implement like this:

export default class PersonList extends React.Component {
  constructor () {
    super();
    this.state = {
    doctorid: '',
    plandate: '',
    starttime: '',
    endtime: '',
  };
  this.handleChange = this.handleChange.bind(this);
}

handleChange (evt, field) {
  // check it out: we get the evt.target.name (which will be either "email" or "password")
  // and use it to target the key on our `state` object with the same name, using bracket syntax
  
  this.setState({ [field]: evt.target.value });
}

  handleSubmit = event => {
    event.preventDefault();

    const userObject = new FormData();

    userObject.append('doctorid', this.state.doctorid);
    userObject.append('plandate', this.state.plandate);
    userObject.append('starttime', this.state.starttime);
    userObject.append('endtime', this.state.endtime);
  
    axios.post(`http://localhost:80/reacttest/src/api/api?action=apptPlan`,userObject, {
      headers: { 
         'Content-Type': 'multipart/form-data'
      }
    })

      .then(res => {
        console.log(res);
        console.log(res.data);
      }).catch((error) => {
        console.log(error)
    });
    // this.setState({ doctorid: '', plandate: '', starttime: '', endtime:''})
    
  }

  render() {
    return (
      <div>
        <form onSubmit={this.handleSubmit}>
          <label>
            <h5>Person doctorid:</h5>
            <input type="text" name="doctorid" onChange={(event)=>this.handleChange(event, "doctorid")} />
            <h5>plandate</h5>
            <input type="text" name="plandate" onChange={(event)=>this.handleChange(event, "plandate")} />
            <h5>starttime</h5>
            <input type="text" name="starttime" onChange={(event)=>this.handleChange(event, "starttime")} />
            <h5>endtime</h5>
            <input type="text" name="endtime" onChange={(event)=>this.handleChange(event, "endtime")}/>
          </label>
          <button type="submit">Add</button>
        </form>
      </div>
    )
  }
}

Or if you want to receive in your backend in JSON format just add the same header and not use JSON.stringify function just send the object in the Axios function.