There is no FMath::Modulo. or any function in the entire engine base called Modulo at least in the newer versions of the engine.
I’m guessing the main sin function might take in a value based on radians while your function as per the the youtube tutorial you can see that the creator uses sind as in sinus function that takes in degrees.
The base function FMath::Sin uses the generic platform implementation that most likely takes in radians. Hence the wrong outcome.
As for other options it’s tough.
You could have a curve with values (would be more flexible than sin) that you could read the value at a specific time and maybe try linking it to a timer function, but it still would have to update often to seem smooth. It also gives you a timer handle in return that you can use to pause / play & even cancel the timer.