запрос на удаление записи из postgres возвращает статус 500, post и get отрабатывают нормально

Нашёл в интернете пример подключения базы данных Postgres к приложению React с помощью express. Данные из базы по get запросу считываются и отображаются и post запрос тоже нормально отрабатывает, а вот метод delete выдает статус 500

App.js

import React, {useState, useEffect} from 'react';
const App=()=> {
  const [merchants, setMerchants] = useState(false);
  useEffect(() => {
    getMerchant();
  }, []);
  function getMerchant() {
    fetch('http://localhost:3001')
      .then(response => {
        return response.text();
      })
      .then(data => {
        setMerchants(data);
      });
  }
  function createMerchant() {
    let name = prompt('Enter merchant name');
    let email = prompt('Enter merchant email');
    fetch('http://localhost:3001/merchants', {
      method: 'POST',
      headers: {
        'Content-Type': 'application/json',
      },
      body: JSON.stringify({name, email}),
    })
      .then(response => {
        return response.text();
      })
      .then(data => {
        alert(data);
        getMerchant();
      });
  }
  function deleteMerchant() {
    let id = prompt('Enter merchant id');
    fetch(`http://localhost:3001/merchants/${id}`, {
      method: 'DELETE',
    })
      .then(response => {
        return response.text();
      })
      .then(data => {
        alert(data);
        getMerchant();
      });
  }
  return (
    <div>
      {merchants ? merchants : 'There is no merchant data available'}
      <br/>
      <button onClick={createMerchant}>Add merchant</button>
      <br/>

      <button onClick={deleteMerchant}>Delete merchant</button>
    </div>
  );
}
export default App;

index.js

const express = require('express')
const app = express()
const port = 3001

const merchant_model = require('./merchant-model')

app.use(express.json())
app.use(function (req, res, next) {
  res.setHeader('Access-Control-Allow-Origin', 'http://localhost:3000');
  res.setHeader('Access-Control-Allow-Methods', 'GET,POST,PUT,DELETE,OPTIONS');
  res.setHeader('Access-Control-Allow-Headers', 'Content-Type, Access-Control-Allow-Headers');
  next();
});

app.get('/', (req, res) => {
  merchant_model.getMerchants()
  .then(response => {
    res.status(200).send(response);
  })
  .catch(error => {
    res.status(500).send(error);
  })
})

app.post('/merchants', (req, res) => {
  merchant_model.createMerchant(req.body)
  .then(response => {
    res.status(200).send(response);
  })
  .catch(error => {
    res.status(500).send(error);
  })
})

app.delete('/merchants/:id', (request, res) => {
  merchant_model.deleteMerchant(request.params.id)
  .then(res => {
    res.status(200).send(res);
  })
  .catch(error => {
    res.status(500).send(error);
  })
})
app.listen(port, () => {
  console.log(`App running on port ${port}.`)
})

merchant-model.js

const { request } = require('express');

const Pool = require('pg').Pool
const pool = new Pool({
  user: 'my_user',
  host: 'localhost',
  database: 'my_database',
  password: 'root',
  port: 5432,
});
const getMerchants = () => {
    return new Promise(function(resolve, reject) {
      pool.query('SELECT * FROM merchants ORDER BY id ASC', (error, results) => {
        if (error) {
          reject(error)
        }
        resolve(results.rows);
      })
    }) 
  }
  const createMerchant = (body) => {
    return new Promise(function(resolve, reject) {
      const { name, email } = body
      pool.query('INSERT INTO merchants (name, email) VALUES ($1, $2) ', [name, email], (error, results) => {
        if (error) {
          reject(error)
        }
        resolve(`A new merchant has been added: ${results.rows[0]}`)
      })
    })
  }
  const deleteMerchant = () => {
    return new Promise(function(resolve, reject) {
      let id = parseInt(request.params.id)
      pool.query('DELETE  FROM merchants WHERE id = $1', [id], (error, results) => {
        if (error) {
          reject(error)
        }
        resolve(`Merchant deleted with ID: ${id}`)
      })
    })
  }
  
  module.exports = {
    getMerchants,
    createMerchant,
    deleteMerchant,
  }