Keep only dynamic approach and add allow-extra-fields link

Author: Arkalo2

forms.rst

@@ -990,28 +990,19 @@ The extra fields can be injected like this:
         {{ form_row(form.email) }}
 
         {# Hidden field to send additional referral code #}
-        <input type="hidden" name="user_create[referralCode]" value="{{ referralCode }}"/>
+        <input type="hidden" name="{{ form.vars.full_name ~ '[referralCode]' }}" value="{{ referralCode }}"/>
 
         <button type="submit">Submit</button>
     {{ form_end(form) }}
 
 Here, the referral code is an extra field injected at view level.
 
-The field name is composed of form ``user_create`` and the field name ``referralCode``.
-It's automatically generated from the form class name. You can :ref:`override it <changing-the-form-name>`
-
-Or you can use
-
-.. code-block:: twig
-
-    {{ form.vars.full_name ~ '[referralCode]' }}
-    
-to render the form name dynamically
-
 You can get the referral code via ``getExtraData``::
 
     $extraData = $form->getExtraData();
     $referralCode = $extraData['referralCode'] ?? null;
+    
+> Don't forget to set :ref:`allow_extra_fields <allow-extra-fields>` option to ``true`` on your form 
 
 Learn more
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