Dynamical maps of the eccentricities of the two inner planets (e_b, e_c) and fixed values of the argument of pericentre of TOI-1438 b(∆ϖ = ω_c − ω_b). The black filled circle with a white rim shows the location of the solution obtained by modelling with the eccentricities set as free parameters. Small values of the fast indicator log REM characterises regular (long-term stable) solutions, which are marked with black and dark blue colour. Chaotic solutions are marked with brighter colours, up to yellow. The black line represents the so-called collision curve of orbits, defined by the condition: α_b(1 + e_b) = a_c(1 − e_c). The resolution of each plot is 301 × 301 points. Triangles marked 1-3 correspond to the solutions shown in Fig. 9. Also, the labelled grey contours refer to the TTV amplitudes shown in Fig. 10 (details in Section 3.5).