This is one of the most common error a beginner use to face when he tries to connect mongoDB database to the cloud mongoDB Atlas.
To fix this error you just need to take care about the connectivity URI should be having the password. And that password should not contain any special characters. If your password is having a special character like Abc@123 or Abcd!() etc , it is not going to work. The password should be having only alphabets or numbers without any special characters.
If you have added your mongoDB atlas cluster password with a special character you can edit it again by going to the homepage>Database Access >Database Users > Edit > Edit Password > Update User.
That was it! Now you just need to go to the URI again and change the cluster password from there.
Hope it would be helpful !