MongoDB Auth Error running Local on MACOS

Question

I installed Locally on mac. Created user superuser with root privledges as per MongoDB Docs:https://docs.mongodb.com/guides/server/auth/#procedure

> db.createUser({user:"superuser",pwd:"strongPassword",roles:["root"]})
Successfully added user: { "user" : "superuser", "roles" : [ "root" ] }
> show users
{
    "_id" : "admin.superuser",
    "userId" : UUID("f873bafd-8d9b-4d2d-95a2-95d9e05db25d"),
    "user" : "superuser",
    "db" : "admin",
    "roles" : [
        {
            "role" : "root",
            "db" : "admin"
        }
    ],
    "mechanisms" : [
        "SCRAM-SHA-1",
        "SCRAM-SHA-256"
    ]
}

launch it with

resulting in running mongodb instance:

  "ctx":"listener","msg":"Waiting for connections","attr":{"port":27017,"ssl":"off"}}

then I mongo --port 27017 use admin response: switched to db admin here's the kicker: I input db.auth("superuser","strongPassword") and then

0```
This is the output in the running mongod client:
```{"t":{"$date":"2021-03-15T14:41:11.167-05:00"},"s":"I",  "c":"ACCESS",   "id":20251,   "ctx":"conn1","msg":"Supported SASL mechanisms requested for unknown user","attr":{"user":"superuser@admin"}}
{"t":{"$date":"2021-03-15T14:41:11.168-05:00"},"s":"I",  "c":"ACCESS",   "id":20249,   "ctx":"conn1","msg":"Authentication failed","attr":{"mechanism":"SCRAM-SHA-1","principalName":"superuser","authenticationDatabase":"admin","client":"127.0.0.1:51532","result":"UserNotFound: Could not find user \"superuser\" for db \"admin\""}}

Please help me? Seems pretty straightforward what my problem is here. Followed the mongoDb docs exactly, and then just totally failing to see my user. What's the trick here?