Failed to connect to mLab by mongo

I tried to connect to mLab on my terminal when I followed the instruction on the website This is the command that I typed

mongo ds151461.mlab.com:51461/simplelogin -u <dbuser> -p <dbpassword>

This is the result I got:

MongoDB shell version v3.4.4
connecting to: mongodb://ds151461.mlab.com:51461/simplelogin
MongoDB server version: 3.2.13
WARNING: shell and server versions do not match
2017-06-12T19:12:35.498-0400 E QUERY    [thread1] Error: Authentication failed. :
DB.prototype._authOrThrow@src/mongo/shell/db.js:1459:20
@(auth):6:1
@(auth):1:2
exception: login failed

Btw, when I run the local mongoDB, I use mongod to make it work and mongo does not work

via Zuoyang Ding