Observed minus calculated (O-C) diagram of the transit times of K2-328 d, compared to our updated ephemeris (light blue region), as described in Sect. 3.3. The times of the transits observed by K2, Hale observatory, and CHEOPS are shown with the blue, red, and orange symbols, respectively. The predicted ephemeris from A22 and B22 are represented with yellow and red curves and regions. The mean ephemeris obtained by the TTV simulations (Sect. 5) is represented by the gray dashed curve.