hi, thanks for your invitation! if u say (見字請覆), that means the guy already read ur note, so u only need to say ........
Please reply as soon as possible. that is enough.
"(Please) reply upon receipt (of this note/message/mail/etc.)"
"Promptly respond upon receipt (of this note/msg/mail/etc.)"
I found some additional reference: http://forum.wordreference.com/showthread.php?t=393425
Hope that helps.