Error handling in controller (MVC structure)
I advice you forego if checks completely and go for try-catch blocks, and have your verifiers throw exceptions on error. So, you do something like this:

try {
     LoyaltyDomModel::loyaltyVerification($post_data);
     LoyaltyDomModel::setVerify(Yii::$app-&gt;user-&gt;identity, $post_data);

     return  ['body'=&gt;'successfull','status' =&gt; true];
} catch (LoyaltyVerificationException $e) {
     return ['body' =&gt; $e-&gt;getMessage(), 'status' =&gt; 'error']
} catch (UserUpdateException $e) {
     return ['body' =&gt; $e-&gt;getMessage(), 'fields' =&gt; $e-&gt;getFields(), /* you can pass custom info to exceptions, right? */, 'status' =&gt; 'error'];
}


Also, it's not a good idea to return bool in one case ('status' = true) and string in another ('status' = 'error');