I'm trying to make an item that my DM provided.  It's part of a space campaign, and one of the common items is a blaster pistol.  Here are the details I have been given:

• 2D4 radiant damage (unclear if that's 2d4 or 2d4+DEX)
• nonlethal
• one handed
• Range 60/180

I can't seem to find a way to create this.  If I base it off any existing ranged weapon, I can't change the base damage dice or the range.  I can't even see them from the Edit Homebrew page, so it's hard to gauge what is being applied.  I also can't seem to find a way to remove the added ability modifier.  I'd be fine not basing it off an existing weapon but the current tools explicitly do not allow that.

What would be the best route to take to create this item?

It is not currently possible to create any magic items not based on other weapons, and it is not currently possible to change damage dice or range for existing weapons. All weapon attacks automatically apply the appropriate Ability modifier to damage as well, that’s a core rule thing. The best you can do is either:

1. Get it as close as possible and talk to your DM about changing what they gave you to match it.
2. Make it as a Wondrous item an just plain text and create the custom action for it directly on the character sheet.

imo, the best way to make homebrew weapons right now is to start with an existing weapon and then edit it within D&D beyond....not create something out of thin air and then hope that it works with D&D beyond.

That option doesn't work if there is no existing weapon with the stats required.  There is no 2d4 radiant damage ranged weapon with ranges of 60/180.

The item was pulled from a third party published adventure and I am the only one in my group using D&D Beyond with that adventure.  Rather than say something useless like "If it were me I'd simply not do the thing you are trying to do" please just stick with more helpful responses like IamSposta above you did.

Well, it’s really just the range and damage dice that are the problem, not the type of damage. What you have to do is find out if there are any 1d4 (60/180) weapons and I can tell you how to do it.

You can create a custom action in your character sheet. If you are in the action tab, on top right of that window you can see a clickable that says Manage Custom. When you click that you can click Add Weapon and Edit that. You can see the different options you have there. Just play around with it and find out what you gotta click and set to create that custom weapon.

At this point I have everything except for adding 1d4 damage figured out.  The way it's done on other items (say Dragon Slayer Longsword) is to use Damage - Additional - Number of Dice: X - Size of Dice: Y.  It doesn't work.  The way the documentation says you should do it is to use Bonus - Magic - Number of Dice: X - Size of Dice: Y.  That also doesn't work.

Is there a third way to do this since both of the officially used methods do not work?

(Bonus—>Magic—>Fixed Value) is only for setting the +1, +2, +3 bonuses.

(Damage—>Type—>Count—>Die Type) is the way to do it, just like Flame Tongue Greatsword, but it won’t roll on the character sheet yet. The dice roller is new, so they haven’t figured out how to make it do that yet, but that is in fact the correct coding.