To no longer receive notifications for the tahoeId(s) you subscribed to, you can do so by making a POST request to http://galaxy.gateway.cco/DataAlerts/RemoveSubscription with below body.
Simply change the Alert Type and TahoeIds to your desired values.
{
"ClientId": "bd79e87f-56e3-4d8a-d6ab-5443c46540f9",
"SubClientId": "26ec9169-85da-4db0-adf2-fae30bd51059",
"AlertType": "NewAreaCode",
"TahoeIds": [
"G-XXXXXXXXXXXXXXXXXXX"
]
}