Coalescence parameters $B_2$ (left) and $B_3$ (right) measured for antinuclei in Pb--Pb collisions at $\mathbf{\sqrt{{\textit s}_{\rm NN}}} = 5.02$ TeV as a function of the transverse momentum scaled by the mass number. Compatible results are obtained for the nuclei. Each colour corresponds to a different centrality class. The boxes represent the systematic uncertainties, while the vertical lines are the statistical ones. See the text for details.