Two calls players make when they get in each other's way on court. Here is exactly what separates them, and what happens to the score.
A let replays the rally with no point awarded. A stroke awards the point outright to the player who was interfered with.
Squash is played in a shared box, so players getting in each other's way is common. Lets and strokes exist to resolve it fairly.
A let is called when interference happens but it is not clear that either player was seriously disadvantaged - the rally could genuinely have gone either way. The point is simply replayed from the same score.
No harm, no foul - just play the point again.
A stroke is called when the interference clearly prevented a player from making a winning shot, or was more serious - for example, blocking access to the ball, or being struck by a ball that was heading for a winning return.
Instead of replaying the rally, the point is awarded outright to the player who was interfered with.
In officiated matches, a referee decides. In casual and club play, players usually call it themselves - the player who was interfered with appeals, and their opponent agrees or disputes it.
Either way, it is a judgment call no scoring app can make for you. What Scorepion can do is keep the score accurate once you have made the call - undo or adjust a point any time, mid-match.