Homebrew Feat problems

So we are currently pretty long into a custom Zelda DND campaign and I am playing a stone pebblit. A melee character with no weapons that scales via a custom class. A fun thing my DM has recently introduced was a ability that allowed me to change into the ice pebblit. which gives resistance to cold, vulnerability to fire and does 1d4 extra ice damage on attacks. I can also turn back into normal (or in the future maybe into a fire version) which means i need to change often.

So far it was a manual thing I had to add and watch out for, but I wanted to try and add it to automatically apply that damage + resistance/vulnerability on equip or activation.

So I made a feat and under the modifier tab ive been able to easily add the resistance and vulnerability. I also wanted to make the feat an option with ice/normal/fire but as far as ive heard you can only make option actions and not modifiers. so my plan was to just make 2 feats (one for ice and one for fire) and switch the feat everytime i needed to.

But im having problems adding the damage. so far ive tried the modifier "damage" and "melee weapon attack" and added the 1d4 ice to both of them. but none of my weapons (just my stone hands) or even non homebrew weapons like club or something have changed my damage roll. Am I doing something wrong?

I have now tried to copy this post 

https://www.dndbeyond.com/forums/dungeons-dragons-discussion/homebrew-house-rules/76575-how-to-homebrew-your-own-buff-system?srsltid=AYCX9vI4czOcd03c0EQawHnAqiyHDzWq7o4MypNmk6i9NYLjiXuK8LSz

and used the Barbarian Rage example. I used the exact same modifiers which in this post is stated as:

Modifier Type: Damage
Modifier Subtype: Melee Weapon Attacks
Fixed Value: **A**
Duration Interval: 1 | Minute

although I have not used a fixed value but a 1d4. but it will still not work and I am still just as clueless

So Ive just found something out, if I add said item and make the modifier Buff a fixed damage of 4 instead of 1d4 it works. Why does that work but not when I change it to 1d4?

The action is exactly what I was hoping to avoid. I dont want to permanently think about needing to add on 5 different damage modifiers at the same time. we have other things that already arent permanent in the homebrew and needing to keep track of it all was the exact thing i was hoping to avoid. at that point I might as well could just put a reminder in my notes and roll a d4 everytime without an action. :/

EDIT: also the same modifier buff with using 4 fixed damage instead of 1d4 only works on an item and not a trait???

so:

Item: fixed damage WORKS, 1d4 NO

trait: fixed damage NO, 1d4 NO

this makes absolutely no sense.

EDIT 2: so ive just looked through the linked post above again. Apparently this is a bug or missing feature. This has persisted for nearly 7 years which is kind of insane to me. The homebrew is restrictive in itself and then stuff like this doesnt even work. Shame, absolute shame.

For things you switch on and off a lot, it's easier if you make an item instead of a feat, so you can toggle with the "equipped" checkbox.

And the inability to add dice as damage bonuses isn't a bug; it's a feature that wasn't present in 5e at the time they built the site, so they didn't build in support for it. They're currently rebuilding the back end to allow for a lot of features that the site can't currently do. (I do not know if the thing you want is one of them.)