Se ruega respuesta

Se ruega respuesta
 

A reply is demanded/required ????
Reply/response required?

I would just say 'please reply'

If you are asking for a reply in a formal invitation, it is R.S.V.P.

If anything, I would say "reply/response requested". But like Perikles says, R.S.V.P. is customary, as far as invitations go.

I think "R.S.V.P. (Répondez S'il Vous Plaît)" is rather an equivalent to "favor de confirmar (su) asistencia".
To me, "se ruega respuesta" is rather used to request an answer or an acknowledgment of receipt to a letter or a written message. :thinking:

To me both mean the same, said in a different way.

Please = I beg your