Error: Oracle DB Plugin Install

Vault
1

I am attempting to do a POC of Oracle Database credential management with Vault but am running into an issue installing the Oracle plugin.

Vault version: v1.5.5
Plugin version: 0.2.1

I have been following the instructions in this article.

To install the plugin, I am running this command:

vault write sys/plugin/catalog/database/vault-plugin-database-oracle \
sha_256="963d50d72de0ea7512bfde01426b0d4296b726d7b2e097d8918430fec37b12a4" \
command="vault-plugin-database-oracle"

And getting this output:

Error writing data to sys/plugin/catalog/database/vault-plugin-database-oracle: Error making API request.

URL: PUT http://127.0.0.1:8200/v1/sys/plugin/catalog/database/vault-plugin-database-oracle
Code: 404. Errors:

* 1 error occurred:
        * unsupported path

My environment looks like this:

[root@vault vault]# cat /etc/systemd/system/vault.service
[Unit]
Description=vault service
Requires=network-online.target
After=network-online.target
ConditionFileNotEmpty=/etc/vault/config.json

[Service]
User=vault
Group=vault
EnvironmentFile=-/etc/sysconfig/vault
Environment=GOMAXPROCS=2
Restart=on-failure
ExecStart=/usr/bin/vault server -config=/etc/vault/config.json
StandardOutput=/opt/vault/logs/output.log
StandardError=/opt/vault/logs/error.log
LimitMEMLOCK=infinity
ExecReload=/bin/kill -HUP $MAINPID
KillSignal=SIGTERM

[Install]
WantedBy=multi-user.target

[root@vault vault]# cat /etc/vault/config.json
{
  "listener": [{
    "tcp": {
      "address" : "0.0.0.0:8200",
      "tls_disable" : 1
    }
  }],
  "api_addr": "http://172.16.3.4:8200",
  "storage": {
     "file": {
       "path" : "/opt/vault/data"
     }
  },
  "max_lease_ttl": "48h",
  "default_lease_ttl": "12h",
  "ui":true,
  "plugin_directory": "/opt/vault/plugins"
 }

[root@vault ~]# echo $VAULT_ADDR
http://127.0.0.1:8200

I am a total newbie at Vault and could use a pointer or two. Am I missing something obvious?

Thanks!