Above all, your RSVP card wording needs to have a space for your guests to respond.
You can leave this section as simple as using “accepts” and “regrets”, but there are many other options. Luckily, you’re able to have some fun with it. Spice it up a little with “happily accepts” and “regretfully decline”, or you can change it up completely with something like “can’t wait to celebrate” and “we will be there in spirit.”
Along with the accept/regret, you have the option of asking them how many people are coming or even making it clear how may people were invited. A few examples: “We have reserved _ seats in your honor,” “Number of guests attending _,” or “_ guests attending out of _.” Some of those blanks would be pre-filled.