I mimicked the configuration that I saw in the Fireball spell, adding an "At Higher Levels" entry of the type "Additional Points". However, when I prepare the spell, the damage doesn't change as the spell level increases: it remains 1d6 + spellcasting modifier at every level.
I created the following homebrew spell: https://www.dndbeyond.com/homebrew/creations/spells/1620322-accelerate-decelerate
I mimicked the configuration that I saw in the Fireball spell, adding an "At Higher Levels" entry of the type "Additional Points". However, when I prepare the spell, the damage doesn't change as the spell level increases: it remains 1d6 + spellcasting modifier at every level.
Never mind. It looks like there was just some delay in the changes propagating to the character sheet.