The rules
Spots is a tally. Nothing about it is worked out from the scores. The count is the record: if the scorer puts two spots against your name on the 7th, you made two spots on the 7th.
What counts as a spot
Anything the group agrees on, as long as it is something the scores cannot show. The app does not know you were in a bunker or hit a tree, which is why the scorer enters it by hand.
Five ways to settle
The stake is set once for the round. What it means depends on the method.
A golfer only pays or collects on the holes he played. Losses can also be capped per golfer for the round.
Scoring it without a spreadsheet
On a paper card, spots end up as ticks in the margin, and by the 15th nobody is sure whose they are. Halved puts a counter under each golfer on the score entry screen, one tap per spot, and settles the counts with the rest of the round.
Every sandy, on the card.
Free for the group. Tap each spot as it happens and Halved settles it alongside the rest of the round.