Creating an Event with a related Lead

Creating an Event with a related Lead

I can't create an Event with a related Lead.

I include these two fields with my xmlData parameter but the field does not populate:

  1.         <FL val="RELATEDTOID">2111963000000333438</FL>
  2.         <FL val="SEMODULE">Leads</FL>

I can only add a Related To Lead on the website, not through the API. I've tried using the lead's full name but nothing seems to work.

Any help very much appreciated.