after deploying app, following error displays. any suggestion to correct this error

npm WARN config production Use --omit=dev instead.

backend@1.0.0 start

node server.js

Server is running on port 6911

Error: connect ECONNREFUSED ::1:587

at TCPConnectWrap.afterConnect [as oncomplete] (node:net:1555:16) {

errno: -111,

code: 'ESOCKET',

syscall: 'connect',

address: '::1',

port: 587,

command: 'CONN'

}