Previously, I was not using $model->save() function for inserting or updating any data. I was simply using createCommand() to execute query and
You are doing all staff correct. I think u must add one line for confirm password validation
if(!$CheckExistingUser) {
$auth_key = $model->getConfirmationLink();
$password = md5($post['password']);
$registration_ip = Yii::$app->getRequest()->getUserIP();
$created_at = date('Y-m-d h:i:s');
$model->auth_key = $auth_key;
$model->password = $password;
$model->confirm_password= md5($post["confirm_password"]); /// add this line
$model->registration_ip = $registration_ip;
$model->created_at = $created_at;
And Also after this condition check model attributes and error like this :
if($model->save()) {
print_r("asd");
}else{
var_dump($model);exit;}