axios does not send post request to server via http-proxy-middleware

import axios from 'axios';

axios
  .post('api/email', { id: 1 })
  .then((res) => {
     return res.data;
  })

server.js

const express = require('express');
const next = require('next');
const { createProxyMiddleware } = require('http-proxy-middleware');
const port = parseInt(process.env.PORT, 10) || 3000;
const dev = process.env.NODE_ENV !== 'production';

const app = next({ dev });
const handle = app.getRequestHandler();

const apiPaths = {
  '/api': {
    target: 'http://localhost:8080/',
    pathRewrite: {
      '^/api': '/api',
    },
    changeOrigin: true,
  },
};

const isDevelopment = process.env.NODE_ENV !== 'production';

app
  .prepare()
  .then(() => {
    const server = express();

    server.use(express.json());
    server.use(express.urlencoded({ extended: false }));
    if (isDevelopment) {
      console.log('ok');
      server.use('/api', createProxyMiddleware(apiPaths['/api']));
    }

    server.all('*', (req, res) => {
      return handle(req, res);
    });

    server.listen(port, (err) => {
      if (err) throw err;
      console.log('> Ready on http://localhost:' + port);
    });
  })
  .catch((ex) => {
    console.error(ex.stack);
    process.exit(1);
  });

My server is located at localhost: 8080.
I write the client side in nextJS and when url calls, I use the http-proxy-middleware package. That is, all my requests that contain / api / will be redirected from localhost: 3000 to localhost: 8080. axios does not send post request, get is fine.
When viewing the Network tab in a developer mode browser, it shows the request headers itself, but without the method. The timing tab displays Caution request is not finished yet.

UPD: I just tried sending via fetch, the result is the same, but I also removed Content-Type: 'application / json' and fetch worked for me. But why is this and how can I solve this?