Connection problem to mongoDB with nodeJS - node.js

Question

I host a Mongo database on an ubuntu server. I created an admin user in order to be able to connect with Nodejs to create a database, add tables, etc. I can connect with mongoDB compass without problems but from nodeJS mongo returns an error.
connect function:
const mongoose = require("mongoose");
mongoose.set("strictQuery", true);
//connect to db
mongoose
.connect("mongodb://" + process.env.DB_USER_PASS + "#2.56.247.250:27017/?authMechanism=DEFAULT")
.then(() => console.log('Connecté a la base de donné'))
.catch((err) => console.log("Erreur de connexion :", err));
Here is the error:
Erreur de connexion : MongoServerError: Authentication failed.
at Connection.onMessage (C:\Users\arnau\Desktop\messIO\node_modules\mongodb\lib\cmap\connection.js:230:30)
at MessageStream.<anonymous> (C:\Users\arnau\Desktop\messIO\node_modules\mongodb\lib\cmap\connection.js:61:60)
at MessageStream.emit (node:events:513:28)
at processIncomingData (C:\Users\arnau\Desktop\messIO\node_modules\mongodb\lib\cmap\message_stream.js:125:16)
at MessageStream._write (C:\Users\arnau\Desktop\messIO\node_modules\mongodb\lib\cmap\message_stream.js:33:9)
at writeOrBuffer (node:internal/streams/writable:392:12)
at _write (node:internal/streams/writable:333:10)
at Writable.write (node:internal/streams/writable:337:10)
at Socket.ondata (node:internal/streams/readable:766:22)
at Socket.emit (node:events:513:28) {
ok: 0,
code: 18,
codeName: 'AuthenticationFailed',
connectionGeneration: 0,
[Symbol(errorLabels)]: Set(2) { 'HandshakeError', 'ResetPool' }

Answer 1

The error AuthenticationFailed means that there is a problem with your connection string and your driver cannot connect into it.
Check for all details here: https://www.mongodb.com/docs/manual/reference/connection-string/
Potential problems:
Special Chars: From the docs: If the username or password includes the following characters: / ? # [ ] # those characters must be converted using percent encoding.
username:password format check that your environmental variable is on the right format, with : between username and pass, and no spaces.
Check your auth database: When you created the user, you created on default ("admin" db is the default.) or created on a specific db, using the command use dbname. If you created on a specific db, you might need to add the auth db name on the connection string.
You can try all the above solutions, making a connection using the mongosh command, to verify that your connection string is fine.