Optimistic update or wait

Pixel 10

Choose

Liking a post must feel instant: p99 under 100 ms on 4G (65 ms round trip). At 0:20 the API is down for 15 s while 120 likes/s arrive. Pick how the app sends a like. No like may be lost and no tap may fail. Budget: 40 USD/month.

Goals

Not tested yet

99 of 100 requests finish faster than this.Saved data that was lost later.The share of requests that fail or get no answer.What the servers and services cost each month.
Choose a design
Wait for the server, then show the like
Show the like at once and send it once in the background
Show the like at once, keep it in an outbox and retry until the server accepts it