I attempted to add a modifier to my homebrew wondrous item and selected "Spell Slot Increase" from the Modifier Type* (required field) dropdown. I then attempted to select a Modifier Subtype* (required field), but the dropdown returned "No matches found". 

This caused a required field error and prevented me from being able to save my modifier to my item.

Note: I would include screenshots, but the image uploader on this forum seems to not work...

I am receiving the same error. I saw a post from August about the feature not being implemented yet but would be later. No idea when later is though.

Very strange. I am trying to add a spell slot to a shield and I get the following.

Edit -Got it.

FYI, I'm also having the same issue with adding the Modifier:  "Weapon Property"

I'm also getting the same issue with Modifier Type: Feat. Nothing shows in the Modifier Subtype field.

I don't even see Weapon Property in weapons created from scratch. I can have "Weapon Property: Finesse" if I make a copy of Sun blade, for example, and I can see it in the modifiers list of that weapon (and edit it, although there's nothing there other than "Finesse"), but the "weapon property" itself doesn't even appear in the modifier type dropdown of a non-copied custom weapon. :/

Was Spell Slot Increase removed in the last update? I was having this issue but since the last update I don't even get Spell Slot Increase as an option in the type dropdown.

The best way to fix a bug... remove the entire feature? 

I’m new to Dnd Beyond and trying to create an item that increases spell slots.  Is this currently possible?

Quote from Stormknight >>

Could be some sort of permissions issue?

This is what I see when I try to add a Modifier as you described.

Also, I generally uses a 3rd party image hosting site like imgur.

I'd love to see this feature revived.  Several items in my campaign have extra spell slots.   It makes using the view as my PC sheet more difficult.

Agreed, currently working around the missing feature with a charge counter. Please revive the feature.

Thanks Stormknight

Anyone heard of this is being reintroduced?