Property 'length' error

Hi,
The page generates the error "Cannot read property 'length' of undefined" associated with the code "if (required_parent.length> 0)"

The plug-in code has not been modified.

I attach a screenshot of the plug-in error and the configuration.

Did you create your form using the designer ? or using custom code ? if its using the designer then did you change the form theme ?

Regards,
Max