I've created a homebrew weapon, and a homebrew spell. The weapon has 1d6 psychic damage from a spell on hit.

What I'm trying to do is to get the weapon to add a 1d6 at levels 5, 11, and 17. I added that to the spell already, but that didn't work. What I did next was to just add the 1d6 as a Spell Scale, which would have been an ok workaround, considering it's just for my campaign.

But when going to the weapon's spell section and changing the "Cast At Spell Level" to 2, which in theory should add 1d6, it doesn't change. My weapon is still at 1d6 regardless of what I do.

How can I make this work properly without changing the spell?

If you've added an extra d6 at levels 5, 11, and 17, would you not need to ask it to cast at level 5 to see the first extra d6?  The spell at level 2 would still be the base spell, no?

So there are three different setting for spells at additional levels: Character Level, Spell Scale, and Spell Level.

The first one I had tried was Character Level (5, 7, 11). I set the Cast At Spell Level to 5, and then to 11, and then 17. None of those made a difference, they all returned at 1d6 instead of the corresponding dice I had set (my character is level 8).

I then tried Spell Level (2, 4, 6, 8 — just to try them out). I set the Cast At Spell Level to 2, then 4, you see where I'm going. None of those worked either.

So, lastly, I set it to Spell Scale (you set it at the interval. In this case, I set it to 1, so at every level it would go up by 1d6. Again, as a test). And once again, this didn't work when changing the Cast At Spell Level to 2 in this case, so it could bump up to 2d6.

At this point, to get it working, I just went in to the spell, changed the base to 2d6, and will have to delete my weapon at levels 11 and 17, change the base of the spell, then re-add my weapon for it to show up properly at the correct amount of dice.

I'm confused on what you're trying to do? 

So you have a weapon and it casts a spell on a hit (or is the spell just your way of getting extra damage to show up for easy rolling)?

What, from an in-game (not character sheet) perspective are you wanting to accomplish with this weapon?

Quote from Necronar >>

I've created a homebrew weapon, and a homebrew spell. The weapon has 1d6 psychic damage from a spell on hit.

What I'm trying to do is to get the weapon to add a 1d6 at levels 5, 11, and 17. I added that to the spell already, but that didn't work. What I did next was to just add the 1d6 as a Spell Scale, which would have been an ok workaround, considering it's just for my campaign.

But when going to the weapon's spell section and changing the "Cast At Spell Level" to 2, which in theory should add 1d6, it doesn't change. My weapon is still at 1d6 regardless of what I do.

How can I make this work properly without changing the spell?

 None of what you want is possible.

Weapons cannot automatically add spell damage on a hit.

Weapons cannot automatically improve based on character level.

Weapon Base Damage cannot be altered.

Yes, I want a hit to trigger a spell stored in a weapon, when a charge is used (3 charges). I want that spell to increase in the damage it does based on the character's level. But that's not the problem I'm having. The problem is that I can't get the spell level to coincide with what I'm putting the spell's casting level as (See post below this one - I included an image). The "Cast At Spell Level" isn't working, regardless of the spell level I'm entering.

What I want should be possible because it's implemented into the system.

#1. It's not automatic, a charge needs to be used, and it is integrated into homebrew weapons that you can use spells on a magical item. There's a whole subsection for spells where you can add the spell.

#2. I don't want the weapon to improve, I want the spell to adjust based on the level. BUT, that is not the problem I'm having. The problem I'm having is that the spell's level isn't adjusting based on the character, currently. I'm setting the weapon to be used as a Level 2 spell in the Homebrew weapon, but it's still only showing up at as a Level 1 spell. In the spells subsection, there is a field for "Cast at Spell Level". I have entered "2", but the weapon still reads a level 1 spell, regardless of what I change it to. The "Cast at Spell Level" isn't effecting anything, currently.

#3. I'm not changing the weapon base damage.

1. Yes you can add spells. No, you cannot make those spells cast in a “hit” with anything other than plain text because a DDB character sheet is not designed to interact with anything other than the DM’s dashboard in the combat tracker, nothing else, so it has no clue who or what you are attacking and therefore no way to know when a “hit” is scored. It will still be up to the player to spend that charge, and cast that spell. Keep in mind, the spell won’t actually interact with anything either. It will still all rely on the player verbally informing the DM what is happening. (Unless you use one of those extensions, but those have nothing to do with this system.
2. Magic items are not designed to pull levels for anything from their wielder. If your “Sinful Smite” is a 1st-level spell, then spending 1 charge will cast it at 1st-level. If you put the Min— Max charges range at 1 — 5  for a 1st-level spell, it’ll cast that spell at 1st-level for 1 charge, and at 5th-level for 5 charges. That is how they are designed. To have it cast at 2nd-level I suggest setting the charges at 2 — 2. (I am assuming you have another, 1st-level spell attached to the weapon currently?) So, since neither the weapon, nor the spell attached to it can “improve” based on anything pulled from the PC…. Get it?
3. I was letting you know that is not an option as a way to mimic what you want in a different way.

In the end, the player will have to spend the charge(s), hit the cast button, roll the spell damage separately, and then inform the DM what was rolled.