The second one, it has a capital letter and a full stop which is needed.
Some problems that might occur is that you might forget some schedules, cause there is going to be several schedules, or you might forget something, etc.
Dear (insert name),
I would like to invite you to my birthday party on (insert date) at (insert time). It will be held at (insert location). If you could RSVP at this number (insert number). I hope to see you there
Your Friend,
(insert name)