Place it immediately after the failed moment, then follow it with a SpongeBob fail cue for a bigger comic drop or a dramatic dun dun dun sting when the letdown needs more weight.
About this sound
This is a soft, cartoon-style sigh lasting less than a second, the kind of quick exhale a character makes when something goes wrong. It feels deflated and gently funny, like giving up without making a fuss. The sound comes from Animal Crossing, where short vocal emotes show a character's mood during play.