Cancel a spell cast

[Walkerbo]

Hi all

I have a list of spells, (hearthstones), that I want to cancel during it's cast.
This is a secure action so I have set up the button as a SecureActionButtonTemplate.

if event == "UNIT_SPELLCAST_SENT" then
    unit, _, _, spellID = ...
    if unit == "player" then
        for k, v in pairs(hearthtonesList) do
            if spellID == v then
                print("found") -- debug --
                b.hiddenSpellStopButton:Click() 
            end
        end
    end
end
 
b.hiddenSpellStopButton = CreateFrame("Button", nil, nil, "SecureActionButtonTemplate")
b.hiddenSpellStopButton:RegisterForClicks("AnyDown")
b.hiddenSpellStopButton:SetAttribute("type", "macro")
b.hiddenSpellStopButton:SetAttribute("macrotext", "/stopcasting")
b.hiddenSpellStopButton:SetScript(
    "OnClick",
    function()
        print("here i am") -- debug --
    end
)
b:RegisterEvent("UNIT_SPELLCAST_SENT")

I get both of the prints, so I can confirm that the button does click yet the spell does not stop the cast.

I have been banging away for the last few days trying to get this working.

Is there a way to stop a cast?