SvelteKit req.body undefined

I'm trying to set up SvelteKit to use it with my CMS.

I'm fetching data from my CMS in api/query.js, and fetching data from api/query in index.svelte.

It works great and I can get the whole data, but I get an error "Cannot read property 'split' of undefined" if I include body in the fetch request. Code:

// api/query.js
export async function post(req) {
  const url = API_URL;
  const auth = Buffer.from(`${API_USER_EMAIL}:${API_USER_PASSWORD}`).toString('base64');

  const res = await fetch(url, {
    method: 'POST',
    headers: {
      'Authorization': `Basic ${auth}`,
    },
    body: JSON.stringify(req.body),
  });
  const data = await res.json();

  return {
    status: data.code,
    body: data
  }
}

// index.svelte
export async function load({ fetch }) {
    const res = await fetch('/api/query', {
        method: 'POST',
        // body: JSON.stringify({
        //  query: 'site.title',
        // }),
    });
    const data = await res.json();

    return {
        status: data.status || 200,
        props: data
    }
}

The commented out portion of code is one that's causing an error. If I console.log(req.body) in api/query.js it returns undefined.

Is there a way I could use Express.js body-parser? Or is there any other way to resolve this error?