[racket] question on uri encode decode

Give a byte string, for example   (bytes 211) , how do I encode it to
"%D3" , using uri-encode , or
any other existing function in racket.

Also when i try to do (uri-decode "%D3") , it complains that :
 "bytes->string/utf-8: string is not a well-formed UTF-8 encoding: #"\323"

Thanks