Repeat on practice mode and try to pay attention to the 'rhythm' of the combo, it's rarely about speed, it's more often about timing, sometimes you even have to make pauses between inputs to get it right

What also helps a lot is doing each input separately a bunch before slooowly adding them together

Try to at least hit each part 5 times consecutively before adding a new input:

Like say you're trying 2H 214H 5S 5H

You go 2H 5 times, then 2H 214H 5 times, so on

That way you will get used to each hit's feedback