A fast pace of growth in deposits and "record member growth" over the December half suggests that the busy investment in "digital" is making its mark at CUA - Australia's largest credit union.Lower interest margins held down CUA's profit for the six months to December 2018, which fell 20 per cent to A$23.1 million.Retail deposits lifted six per cent to $9.7 billion, reflecting themes of the mutual's advertising spending last year, said Rob Goudswaard, CUA's CEO.CUA said it settled $2.3 billion in new loans during the half, up 79 per cent.Net member growth CUA said was 16,996 "taking total members to a record 490,126".Its instant messaging app iM CUA is now available to all members. CUA claims the app "is the first in Australia to allow members to choose their own personal banker" and flows from a collaboration with US bank Umpqua and Dutch bank de Volksbank.Goudswaard said there was "still a significant education required for members to understand the New Payments Platform", with enrolments in PayID now at around 23,000 members.