CF8 - PHP Action - Textfield

I have a PHP action. This returns either D or M. For M I need an optional text field, for D I need a mandatory text field. How do I solve this?

By using the Events behavior, with 2 events D,M, in D add a text field with no "required" validation, and in M add another with "required" validation

OK, that's how I implemented it. I also see the text field without "required validation". But, I can't submit the form! Message: "This field is required" (from hidden text field) Would you like to recreate this for yourself?!

Hello Max, it works... thank you very much...