I disagree; a message sent on an async platform is not expected to be responded to immediately, it's simply meant to be removed from the sender's "to-do" list.
The distinction between sync vs async messaging isn’t as easy to figure out these days as it was when snail mail vs phone call were the primary options.
The negative consequences of making the wrong choice are both extremely low and extremely loud, so I urge you to just take a guess, with a strong bias for every technology platform being async.
