PJ here, Soundslice designer. I'm pretty sure your issue is that to add a note, you have to hover over the particular string you want to add the note to while y

PJ here, Soundslice designer. I'm pretty sure your issue is that to add a note, you have to hover over the particular string you want to add the note to while you have a selection. You can also press 'A' to add a note to the next available string. Does that help?