UIDropDownMenu doesn't show

[Benalish]

The goal is create a custom combobox template, where the dropdown menu appears with the click on the button. I followed this guide, but the UIDropDownMenu is not shown when button is clicked.

XML code:

<Frame name="combobox_template" virtual="true">
	<Size x="1" y="1" />
	<Frames>
		<EditBox name="$parentEditbox" parentKey="editbox">
			<Size x="125" y="18" />
			<Anchors>
				<Anchor point="CENTER" >
					<Offset>
						<AbsDimension x="27" y="5"/>
					</Offset>
				</Anchor>
			</Anchors>
			<Backdrop bgFile="Interface\Buttons\WHITE8X8" edgeFile="Interface\Buttons\WHITE8X8" tile="true">
				<EdgeSize>
					<AbsValue val="1"/>
				</EdgeSize>
			</Backdrop>
			<Scripts>
				<OnLoad>				
					self:SetBackdropColor(0, 0, 0, 0.75)
					self:SetBackdropBorderColor(0.3, 0.3, 0.3, 1)
					self:EnableMouse(false)
					self:EnableKeyboard(false)
				</OnLoad>
			</Scripts>
			<Frames>
				<Button name="$parentButton" parentKey="button" enableMouse="true">
					<Size>
						<AbsDimension x="25" y="25"/>
					</Size>
					<Anchors>
						<Anchor point="RIGHT" relativeTo="$parent" relativePoint="RIGHT">
							<Offset x="3" y="0"/>
						</Anchor>
					</Anchors>
					<Scripts>
						<OnMouseDown> flag_dd_OnClick() </OnMouseDown>
					</Scripts>
					<HighlightTexture file="Interface/Buttons/UI-Common-MouseHilight" alphaMode="ADD"/>
					<NormalTexture file="Interface/CHATFRAME/UI-ChatIcon-ScrollDown-Up" setAllPoints="true"/>
					<PushedTexture file="Interface/CHATFRAME/UI-ChatIcon-ScrollDown-Down" setAllPoints="true"/>
				</Button>
				<Frame name="flag_dd" inherits="UIDropDownMenuTemplate">
					<Scripts>
						<OnLoad>
							UIDropDownMenu_Initialize(self, flag_dd_OnLoad, "MENU");
						</OnLoad>
					</Scripts>
				</Frame>
			</Frames>
		</EditBox>
	</Frames>
</Frame>

Lua code:

local main = CreateFrame("Frame", nil, UIParent)
main:SetSize(200, 100)
main:SetPoint("CENTER")
main:SetFrameStrata("HIGH")
local backdrop = {
    bgFile = "Interface\\DialogFrame\\UI-DialogBox-Background",
    edgeFile = "Interface\\Tooltips\\UI-Tooltip-Border",
    tile = true,
    tileSize = 8,
    edgeSize = 16,
    insets = {
        left = 3,
        right = 3,
        top = 3,
        bottom = 3
    }
}
main:SetBackdrop(backdrop)
 
main.conditions = CreateFrame("Frame", nil, main, "combobox_template")
main.conditions:SetSize(125,25)
main.conditions:SetPoint("CENTER")
 
function flag_dd_OnLoad(frame, level, menuList)
    local info = UIDropDownMenu_CreateInfo()
    info.text = "Blue Pill"
    UIDropDownMenu_AddButton(info)
    info.text = "Red Pill"
    UIDropDownMenu_AddButton(info)
 end
 
function flag_dd_OnClick()
    ToggleDropDownMenu(1, nil, flag_dd, "cursor", 0, 0);
end