I'm trying to create a custom homebrew spell for a campaign. It is a level 5 spell. I have set the damage modifier to 8d6 fire damage (under the modifier heading), and have set higher level scaling to Spell Scale. Under the Higher Levels heading, I have set level to 1, modifier to the 8d6 Fire damage, additional points, 3d6. The problem is, when I give the spell to my character, it comes up showing the damage as 3d6.

How would I fix this? I've tried removing the higher level scaling thing, and that didn't work, so I don't know what I'm doing wrong.

Hey, i know its been a while. But I had the same Problem. I homebrewed it looking at Fireball but it is for some reason wrong. When you add Higher level scaling don't choose "Additional Points" but "Additional Count" and it should work.
Wrong Solution @IamSposta helped finding my error (comment below)

“Additional count” would increase the number of fireballs by “3d6” per spell level, “additional points” is the correct spell scale to use. They must have had a different problem. Tell me, did you use Fireball as a template, or just reference it?

I did just reference it. I missed the Option "higher level scaling type" under the "basic information" group directly next to "available for class(es)". Had it on "spell level"...

Now everything is working perfectly. Thanks for the notice.