Create a function for a trigger, but I'm getting a syntax error on the "RETURN NEW;" line

Question

CREATE OR REPLACE FUNCTION update_summary_table()
RETURNS TRIGGER AS $$
BEGIN
    -- Insert or update the summary table with aggregated data
    INSERT INTO summary_table (movie_title, total_rentals, total_revenue, average_rental_duration, rental_month)
    VALUES (
        NEW.movie_title, -- New movie title
        1, -- Initial rental count
        NEW.payment_amount, -- Initial revenue
        EXTRACT(DAY FROM NEW.return_date - NEW.rental_date), -- Rental duration in days
        DATE_TRUNC('month', NEW.rental_date) -- Rental month
    )
    ON CONFLICT (movie_title, rental_month) -- Handle conflicts for the same movie and month
    DO UPDATE
    SET 
        total_rentals = summary_table.total_rentals + 1, -- Increment rental count
        total_revenue = summary_table.total_revenue + NEW.payment_amount, -- Add to total revenue
        average_rental_duration = (
            (summary_table.average_rental_duration * summary_table.total_rentals + EXTRACT(DAY FROM NEW.return_date - NEW.rental_date)) 
            / (summary_table.total_rentals + 1) -- Recalculate average duration
        );

    -- Return the new row to allow the trigger to proceed
    RETURN NEW;
END;
$$ LANGUAGE plpgsql;

Verified all column names match. not sure what else to try.

Exact Error: