Validation Rules Group Error

I have a 4.0.4 project i am trying to port to 4.3.1 and so far so good except I am getting the error:
I believe 'login' is referring to my controller method authentication/login
 

Code:

login is not a validation rules group

The offending line is here... was there a change between 4.0.4 and 4.3.1 that broke this?

PHP Code:

if (!$validation->withRequest($this->request)->run($_POST, 'login')) { }


The entire error stack:

Uncaught Error.
{
    "title": "CodeIgniter\\Validation\\Exceptions\\ValidationException",
    "type": "CodeIgniter\\Validation\\Exceptions\\ValidationException",
    "code": 500,
    "message": "\"/login\" is not a validation rules group.",
    "file": "/var/www/vhosts/mydomain.com/dev.mydomain.com/vendor/codeigniter4/framework/system/Validation/Validation.php",
    "line": 619,
    "trace": [
        {
            "file": "/var/www/vhosts/mydomain.com/dev.mydomain.com/vendor/codeigniter4/framework/system/Validation/Validation.php",
            "line": 619,
            "function": "forGroupNotFound",
            "class": "CodeIgniter\\Validation\\Exceptions\\ValidationException",
            "type": "::"
        },
        {
            "file": "/var/www/vhosts/mydomain.com/dev.mydomain.com/vendor/codeigniter4/framework/system/Validation/Validation.php",
            "line": 118,
            "function": "loadRuleGroup",
            "class": "CodeIgniter\\Validation\\Validation",
            "type": "->"
        },
        {
            "file": "/var/www/vhosts/mydomain.com/dev.mydomain.com/app/Controllers/Authentication.php",
            "line": 44,
            "function": "run",
            "class": "CodeIgniter\\Validation\\Validation",
            "type": "->"
        },
        {
            "file": "/var/www/vhosts/mydomain.com/dev.mydomain.com/vendor/codeigniter4/framework/system/CodeIgniter.php",
            "line": 934,
            "function": "authenticateLoginAjax",
            "class": "App\\Controllers\\Authentication",
            "type": "->"
        },
        {
            "file": "/var/www/vhosts/mydomain.com/dev.mydomain.com/vendor/codeigniter4/framework/system/CodeIgniter.php",
            "line": 499,
            "function": "runController",
            "class": "CodeIgniter\\CodeIgniter",
            "type": "->"
        },
        {
            "file": "/var/www/vhosts/mydomain.com/dev.mydomain.com/vendor/codeigniter4/framework/system/CodeIgniter.php",
            "line": 368,
            "function": "handleRequest",
            "class": "CodeIgniter\\CodeIgniter",
            "type": "->"
        },
        {
            "file": "/var/www/vhosts/mydomain.com/dev.mydomain.com/public/index.php",
            "line": 67,
            "function": "run",
            "class": "CodeIgniter\\CodeIgniter",
            "type": "->"
        }
    ]
} 


---

This is being called from AJAX:

Code:

$.ajax({
    type: 'POST',
    url: base_url + "/authenticateLoginAjax",
    data: {'username': username,  'password': password},
    dataType: 'json',
    success : function(response) {
        console.log(response.errors);
        if (response.errors === undefined || response.errors.length == 0) {
            window.location = response.url;
        } else {
            setTimeout(function() {
                console.log('errors');
                $('.form-row.messages').hide();
                $('.form-row.messages').removeClass('authenticating').addClass('error').fadeIn();
                $('.form-row.messages span').html(response.errors.username);
            }, 2000);
        }
    }, error : function(jqXHR, exception) {
        var message = 'Uncaught Error.\n' + jqXHR.responseText;
        console.log(message);
    }
});
return false;