Please RSVP
The extra please.
RSVP means please respond. It is from French répondez s’il vous plaît. You may put RSVP on the invitation, or you may write the request in English. Do not use Please RSVP. That repeats please.
Examples
UseRSVP by Friday.
UsePlease reply by Friday.
AvoidPlease RSVP by Friday.