I am deploying a full stack application on render. But I don’t know why I am getting this

MongooseServerSelectionError: connect ECONNREFUSED 0.0.0.0:27017
    at _handleConnectionErrors (/opt/render/project/src/node_modules/mongoose/lib/connection.js:897:11)
    at NativeConnection.openUri (/opt/render/project/src/node_modules/mongoose/lib/connection.js:848:11) {
  reason: TopologyDescription {
    type: 'Unknown',
    servers: Map(1) { '0.0.0.0:27017' => [ServerDescription] },
    stale: false,
    compatible: true,
    heartbeatFrequencyMS: 10000,
    localThresholdMS: 15,
    setName: null,
    maxElectionId: null,
    maxSetVersion: null,
    commonWireVersion: 0,
    logicalSessionTimeoutMinutes: null
  },
  code: undefined
}

error in the render logs. My database is also running fine but I don’t know why my application is not running.
I have used this code for my mongodb connection. `

const mongoose = require("mongoose");

mongoose
  .connect(process.env.MONGODB_URI)
  .then(() => {
    console.log("connected");
  })
  .catch((err) => {
    console.log(err);
  });

Thankyou.

My page keeps crashing when I log in