Fetch/Axios await/async not working inside NextJS API

Question

This is working:

function myApi(req, res) {
  fetch(url, opt).then();
}

This not:

async function myApiAsync(req, res) {
  await fetch(url, opt);
}

This causes a memory leak:

async function myApiAsyncAlternative(req, res) {
  await fetch(url, opt).then();
}

I've to note that I'm making a call no another NextJS API inside this API.

With await the function never reaches the next line. It makes the request, because if for example, I skip the headers, I get a 401 error. Neither working with Axios.