Doc link - http://developer.pardot.com/kb/api-version-4/emails/#sending-one-to-one-emails
For version 4, under sending one to one email section shows incorrect version :
Shows the url format as - /api/email/version/ 3/do/send/prospect_id/ <prospect_id>?...
Expected format - /api/email/version/ 4/do/send/prospect_id/ <prospect_id>?...
Same for prospect_email parameter
Actual -/api/email/version/ 3/do/send/prospect_email/ <prospect_email>?...
Expected -/api/email/version/ 4/do/send/prospect_email/ <prospect_email>?...