This video explains how to put slide notes and portamento notes into FL Studio. It also explains why slide notes do not work sometimes when they are placed into the piano roll. Wrongly positioning the slide note gives the impression of a blank or empty note in the piano roll.
Also discussed is the difference between glissando and portamento notes and how that relates to adding notes to the Fruity Loops piano roll. The software used in the demonstration is FL Studio version 20.1.1.