Howto set/get custom ribbon mso:checkbox via VBA in MS Project 2016?

Question

first of all sorry for the probably stupid question, but I am very new to VBA. Here is the question:

I added a simple checkbox in my custom ribbon tab

The MS Project file implements this function:

Private Sub Project_Open(ByVal pj As Project)
    AppInit.Initialize_App
End Sub

I then have a module "AppInit" which defines my functions:

Public g_bIsAutoUpdateSched As Boolean

Public Sub Initialize_App()
    Dim ribbonXml As String

    UpdateSettings

    ribbonXml = "<mso:customUI xmlns:mso=""http://schemas.microsoft.com/office/2009/07/customui"">"
    ribbonXml = ribbonXml + "  <mso:ribbon>"
    ribbonXml = ribbonXml + "    <mso:qat/>"
    ribbonXml = ribbonXml + "    <mso:tabs>"
    ribbonXml = ribbonXml + "      <mso:tab id=""myTab"" label=""CIG"" insertBeforeQ=""mso:TabFormat"">"
    ribbonXml = ribbonXml + "        <mso:group id=""gUpdate"" label=""Update"" autoScale=""true"">"
    ribbonXml = ribbonXml + "          <mso:checkBox id=""cbUpdateSprints"" label=""Auto schedule goals"" getPressed=""Function_Checked"" onAction=""Function_Action"" />"
    ribbonXml = ribbonXml + "        </mso:group>"
    ribbonXml = ribbonXml + "      </mso:tab>"
    ribbonXml = ribbonXml + "    </mso:tabs>"
    ribbonXml = ribbonXml + "  </mso:ribbon>"
    ribbonXml = ribbonXml + "</mso:customUI>"

    ActiveProject.SetCustomUI (ribbonXml)
End Sub

Sub Function_Checked(control As IRibbonControl, ByRef pressed)
    pressed = True
End Sub

Sub Function_Action(control As IRibbonControl, pressed As Boolean)
    g_bIsAutoUpdateSched = pressed
End Sub

I searched the web for this and its implemented the same everywhere (similar to what I did). However when I run my code I get the following error:

Automation error Exception occured.

Removing the arguments from both functions fixes it?

Sub Function_Checked()

End Sub

Sub Function_Action()

End Sub

However that obviously defeats the entire purpose as I want set the default state, and also be able to get the state of that button...

Any help would be appreciated!