It was removed from the addon compatibility aliases files with PTS v8.0 as you can see here:
https://github.com/esoui/esoui/blob/...ityaliases.lua
Should be FindActionSlotMatchingItem(bagId, slotIndex) now as it was the same code that the function returned in that alias, like Sharlikran said already.
As you can see here it is used in ZOs code on PTS 8.0
https://github.com/esoui/esoui/blob/...slot.lua#L1568