[Fizzlemizz]

local function fromGT(self)
    print("Button Clicked!")
    AutoStoreGuildBankItem(1,1);
end
 
UIConfig.GT1toBagButton:SetScript("OnClick", fromGT);

Adding the brackets to fromGT() in the SetScript means you a calling the function then as part of the SetScript rather than telling the SetScript to USE the function when the OnClick script is run.

Added a print so you can see if the function has been called.