I am trying to build a nextjs app. It runs fine on npm run dev but gives this error when I run npm run build

> Build error occurred
FetchError: request to http://localhost:4001/graphql failed, reason: connect ECONNREFUSED 127.0.0.1:4001
    at ClientRequest.<anonymous> (/Users/naweddiwan/Desktop/codinqQuest/next-saas-starter/node_modules/node-fetch/lib/index.js:1461:11)
    at ClientRequest.emit (events.js:400:28)
    at Socket.socketErrorListener (_http_client.js:475:9)
    at Socket.emit (events.js:400:28)
    at emitErrorNT (internal/streams/destroy.js:106:8)
    at emitErrorCloseNT (internal/streams/destroy.js:74:3)
    at processTicksAndRejections (internal/process/task_queues.js:82:21) {
  type: 'system',
  errno: 'ECONNREFUSED',
  code: 'ECONNREFUSED'
}

Can somehelp me, what can be causing this error.