Access form data with custom php code

I have a multipage form and I would like to add some custom PHP validation when moving to the next page on some of the fields.
I have placed a debugger at the start of the second page so that I can see the information I'm getting followed by the php code but, when I try to access $form->data['input-name'] I get a PHP error: "Notice: Undefined variable: form in (...)".

In chronoforms v6 you have to use: $this->data('inputname');

This is going to sound strange but I had done that and it wasn't working for some reason but now it is!
Thank you very much for the quick reply Bob!😀