Declining an invitation carries more weight in people's heads than it should. There is a low hum of guilt, a worry about disappointing the host, a temptation to over explain or to leave it on read and hope it goes away. None of that is necessary. A clean no, given promptly, is one of the most considerate things you can do as a guest.
A quick no beats a slow maybe
The host is trying to plan. A clear no a week out is genuinely more useful to them than a maybe that drifts into a silent absence on the night. You are not ruining their event by declining, you are giving them accurate information to plan around. The thing that actually makes hosting hard is not people saying no, it is not knowing the real number. Your honest decline is a contribution to that, not a problem.
You do not owe a detailed reason
The temptation when declining is to justify it, to build a case so the host knows you really wanted to come. A short, warm no is enough. Cannot make this one, hope it is a great night is a complete reply. Over explaining can actually feel worse to the host, like you are managing their feelings. Trust that a friendly no is received as a friendly no. Most hosts are far less wounded by it than the part of your brain writing the apology assumes.
Use the RSVP, do not route around it
If the invite has an RSVP, use it. Tapping cannot make it is faster for you and cleaner for the host than a separate message they then have to manually reconcile against the list. On PopIn the host just sees your reply on the guest list, and the response is not broadcast to the room, so declining is quiet. You can add a short note if you want to say something warmer, but you are not obligated to compose a message outside the flow.
Maybe is a real answer, used honestly
Maybe gets a bad reputation, but it is a legitimate reply when you genuinely do not know. The problem is only when maybe is used to avoid the discomfort of a no you already know is a no. If it is truly uncertain, mark maybe and update it when you know. If it is really a no, say no. The host can plan around an honest maybe. They cannot plan around a yes that was always going to be an absence.
Decline now, stay on the list
The quiet fear behind a lot of declining is that saying no often enough gets you dropped. The opposite is true. The guest who replies honestly and promptly, yes or no, is easier to invite than the one who goes silent and leaves the host guessing. A clean no keeps you on the list. A pattern of silence is what slowly takes you off it.