API resolved without sending a response in Nextjs

You should return a Promise and resolve/reject it.

Example:

import { getData } from "../../helper";export default async function(req, res) {  return new Promise((resolve, reject) => {    getData()      .then(response => {        res.statusCode = 200        res.setHeader('Content-Type', 'application/json');        res.setHeader('Cache-Control', 'max-age=180000');        res.end(JSON.stringify(response))        resolve();      })      .catch(error => {        res.json(error);        res.status(405).end();        return resolve(); //in case something goes wrong in the catch block (as vijay) commented      });  });};

import { getData } from "../../helper";export default async function (req, res) {  try {    const response = await getData();    res.statusCode = 200;    res.setHeader('Content-Type', 'application/json');    res.setHeader('Cache-Control', 'max-age=180000');    res.end(JSON.stringify(response));  }  catch (error) {    res.json(error);    res.status(405).end();  }}

You can use 'next-connect' library which eliminates the necessity of returning a promise in this scenario. If you like express.js's route->middleware->endpoint pattern this library is what you are looking for. It also provides global error handling out of the box! [next-connect docs]

Example:

import nc from 'next-connect'function onError(err, req, res, next) {  logger.log(err);  res.status(500).end(err.toString());  // OR: you may want to continue  next();}const handler = nc({ onError });handler  .use((req, res, next) => {    if(!req.user){      throw new Error("oh no!");      // or use next      next(Error("oh no"));    }  })  .get((req, res) => {    res.end("success")  })