SecureActionButtonTemplate with macrotext attribute not working

[Zax]

None of my secure buttons with macrotext attribute are working on PTR 10.x

In the main XML file (MyAddon.xml):

<Frame name="npcm_frameMain" frameStrata="BACKGROUND" virtual="false" hidden="true" resizable="true" parent="UIParent" inherits="SecureHandlerStateTemplate">

In the main lua file (MyAddon.lua):

local button = CreateFrame("Button", "secureBtnTest", npcm_frameMain, "SecureActionButtonTemplate")
button:SetSize(32,32)
button:SetPoint("LEFT", npcm_frameMain, "RIGHT", 300, 0)
local texture = button:CreateTexture("$parent_tex", "BACKGROUND")
texture:SetAllPoints(true)
texture:SetTexture(GetSpellTexture("Forme de Voyage"))
button.texture = texture
    
button:SetAttribute("type", "macro")
button:SetAttribute("macrotext", "/sit")
button:SetScript("PostClick", function(self, arg1)
    print(self:GetName(), arg1, self:GetAttribute("macrotext"))--testing
end)

Nothing happens when the button is clicked (and no error message nor warning about blocked action).
Thank you for your help.