Hey @Piotr 

Welcome to the Klaviyo Community! Happy to help with your legacy form.

The $method_id  and $method_type are used to specify the form type (embed, popup or flyout). However you will only need to use these fields if you are creating an embedded legacy signup form. If you are creating an embedded signup form you can follow the document I linked and use the code given verbatim.

I linked the help center articles for popups and flyouts as well if you aren’t using an embed form.

Hope this helps and thank you again for joining the Klaviyo Community!

Thank you very much.