Sentence:  If you are unable to sign the request , because of illness or other good cause , another person who stands in close personal or business relationship to you may sign the request on your <WSD>behalf</WSD> , stating the reason why you are unable to sign . 
Meaning of the word marked with <WSD> tags:  as the agent of or on someone's part (usually expressed as "on behalf of" rather than "in behalf of");