After double checking with other players in the Paladin forum I find there's a gap in how the Character Sheet handles Divine Smite.  It's not a spell so it's not listed in the Spells section, it's in Actions, Other.  However, I find that to be a relatively buried section.  I can't use the "Cast" feature (or activate, or use, or whatever) and it doesn't cross reference my available spell slots and does not allow me to roll damage from where it's located unlike a proper spell.  

Considering how often it's used by Paladins I believe it deservers more prominence on the character sheet with the functionality mentioned above.

Thanks!

+1 to this... especially now with the integrated dice roller. I added a custom action to roll the 2d8, but would be nifty to have it built in and integrated with spell slot tracking.

In interim there is a workaround: make a homebrew spell for it. This way, not only can you roll it in a single a click, but it'll scale by slot level used and check off the spell slot. 

So I had a notification of a reply to me asking about me making this spell suggestion. I didn't respond right away, I wasn't well, but I've come back to find it's gone now? In any case, I did it. I can't publish it, sorry, as it would be recreating a published feature and using spells in a way not actually meant for, well, spells. It's just a workaround for convenience, a sort of "sheet cheat" as it were. So, instead I made a guide which I'll post here for you, so you can make it for yourself and apply it to your Mary-Sue Knight Paladins.

This is based on using the website on a PC. You'll have to adjust it accordingly for your device/browser/whatever-it-is that you're using.

So we'll be making a spell. At the menu bar at top click Collections and on the right-side of the submenu that appears choose Create Spell. 

You should see this.

Click on Create From Scratch.

The next page will have lots of boxes. Just edit the ones as follows:

Spell Name: Divine Smite
Spell Level: 1st
Spell School: Evocation
Casting Time: 1 action
Spell Range Type: Self
Duration: Instantaneous
Description: 

Paladin Divine Smite Feature: when you hit a creature with a melee weapon attack, you can expend one spell slot to deal radiant damage to the target, in addition to the weapon’s damage. The extra damage is 2d8 for a 1st-level spell slot, plus 1d8 for each spell level higher than 1st, to a maximum of 5d8. The damage increases by 1d8 if the target is an undead or a fiend, to a maximum of 6d8.

Near the bottom are some checkboxes. Check the box for "At Higher Levels Scaling?" and to the right of this for the drop-down that says "Higher Level Scaling Type" choose "Spell Level". 

At the bottom right where it says "Available for Class(es)" put in and choose "Paladin". It's important to not choose any of the subdomains it brings up. 

Click Create Spell button.

The next page will feature multiple sections for Basic Info, which is essentially the above parts if you need to change anything, Additional Info and then a section for creating options, modifiers, and such.

Click the Additional Information bit and it will expand showing more boxes and stuff. Change the following:

Attack Type: Melee

Then click the Save Changes button.

(We did this so it shows it on the actions section of the Character Sheet)

Now we get to the nitty gritty. Scroll down to Modifiers. You will find the blue Add Modifiers button and a + symbol. The + symbol expands the section to show any created modifiers in case you want to edit or delete one. We don't have any, so get started by clicking the Add Modifiers button.

Another page of boxes. Change the following:

Modifier Type: Damage
Modifier Sub-Type: Radiant
Dice Count: 2
Die Type: D8
Details: +1d8 if the target is an undead or a fiend.

Click Save Changes.

You'll be taken back to the previous page with your modifier now showing in the list. This modifier provides the base damage done when expending a 1st level slot. So, now we need to create the scaling for when higher spell slots are used. So for that, go to the bottom and there is a section for "At Higher Levels". Click the "Add A Higher Level" button.

On this new page of boxes set the following:

Scaling Level Value: 2
Modifier to Scale: Damage - Radiant (3d8)
Scale Effects: Additional Points
Dice Count: 1
Die Type: D8

Click Save

So now our spell does an extra 1d8 (a total of 3d8) when a 2nd level slot is used. You will need to do this for each level a change in damage occurs. So repeat the process for 3rd and 4th levels changing the Scaling Level Value (basically the spell slot level) and the Dice Count appropriately. Remember, at 4th level Divine Smite has reached the cap, so we don't need to add any more levels beyond this. Note that because we are scaling by the type "Spell Level" this means at each Higher Level we are Replacing the damage, so the Dice Count is to represent the damage total for this spell level.

Finally, click Save Changes. 

You're done. Add this to your character. For it to work with spell slots and the like, you will need to edit the subclass your character is using, to make a copy and make a feature and use the Spells section to add it, ensuring "uses spell slot" is on and "counts as known spell" is off. It'll then be added to your character . If anyone struggles let me know and I can make a guide for that too.

 Extra Tips

Once added to character you can see it under actions showing the base dmg. Click it then click Customise and in the Notes box add something like "Use under Spells to check slots / roll higher dmg" - this will remind you to use this under Spells tab so it checks off spell slots and lets you see (and roll if using the virtual dice) the higher damage (you'll need higher level scaling on for the sheet).

Hope this helps.

Thanks everyone... very helpful. I created a homebrew spell and cloned my Paladin Oath subclass and adding the custom spell as a 2nd level class feature. It does not show up under 'Actions | Attack' as Cyb3rM1nd shows above. It shows up under 'Spells' and I can 'cast' it to consume a spell slot, but it doesn't appear under 'Manage Spells' as always prepared. Just another option and works for me... again, thanks for the tutorial to get me started.

Cyb3rM1nd, that was me!  I deleted my post because I thought I was being lazy in that I didn't attempt to try it myself!  lol

However I was stuck on the part where it tops out at 5d8 (6d8 if fiend or undead) and I was going to ask for help on that!  ;)

Thank you very much!!

Another update...it looks like I don't need a custom subclass at all. When you create the homebrew spell, add your subclass to the 'Available for Class(es)' entry and it automatically shows up as an 'Always Prepared' spell. Much simpler. So my spell shows up and I can cast it at first level, but I haven't gotten the spell scaling to work. Taking another poster's advice and waiting 20 minutes for my last changes to propagate (it seems to take a while for all of the backend systems to see homebrew changes).

Thank you so much for this guide!!! I followed jmutchek's add-on below where I added my subclass to the spell. But! Your screenshots do not match up with what shows up for me. When I'm putting in the info for scaling, specifically level 2 where I add 1 additional dice, when I hit save, under dice roll it says 1d8 - not like your screenshot where it says 3d8. I went back and modified the number of dice to 3. Is that right? Was I maybe just reading your directions wrong?

ANYWAY, that's not where I'm even the most confused - I am tripping up at the end where you have:

Finally, click Save Changes. 

You're done. Add this to your character. For it to work with spell slots and the like, you will need to edit the subclass your character is using, to make a copy and make a feature and use the Spells section to add it, ensuring "uses spell slot" is on and "counts as known spell" is off. It'll then be added to your character . If anyone struggles let me know and I can make a guide for that too.

 Extra Tips

Once added to character you can see it under actions showing the base dmg. Click it then click Customise and in the Notes box add something like "Use under Spells to check slots / roll higher dmg" - this will remind you to use this under Spells tab so it checks off spell slots and lets you see (and roll if using the virtual dice) the higher damage (you'll need higher level scaling on for the sheet).

I'm lost with both of these. Can you elaborate? Thank you so much for making this!!!!!

Bump. This very basic class feature should not require this kind of workaround. +1 for fixing this.

"it's never been easier", unless you are a paladin

I realized after making all of this and getting ready to add it to my character… that I’m level 2. I don’t have a subclass yet. I knew which one I was planning to use, so I edited that subclass, but I can’t actually use Divine Smite at 2nd level with a 3rd level class feature like an edited subclass.

Is there a way to make this available before choosing an oath?

Is there any way to update the 'spell' to add the +1d8 for fiend/undead as a toggle choice when you use Beyond20? help/instructions would be most helpful

In case it is more helpful I made a video showing how to add the Divine Smite on the sheet for use with the dice roller.

Thanks for the tutorial!

It's absurd that we have to go through this, but at least we can use some kind of workaround.

You're welcome and I agree. It's quite a lot to do for a workaround and should be implemented by D&D Beyond. But, we have a way to do it until then even if it's annoyingly clunky.