The ${\rm K}^0_{\rm S}\pi^{\pm}$ invariant mass distribution at $|y|< 0.5$ in pp collisions at $\sqrt{s} = 13$ TeV for the $1.6 < p_{\rm T} < 2.0$ GeV/$c$ interval in the VI V0M multiplicity class (black full circles), before (upper panel) and after (lower panel) the uncorrelated background subtraction. Statistical uncertainties are shown with error bars. In the upper panel the red open circles describe the background shape evaluated via the event-mixing technique, while the yellow-filled area represents the normalization region (1.1--1.2 GeV/$c^2$) between the mixed-event background and the same-event pair invariant mass distribution. In the lower panel the solid green curve is the result of the fit with Eq.1, while the dashed red and blue line describe, respectively, the residual background given by Eq.2 and the non-relativistic Breit--Wigner function. The blue regions represent the tails of the non-relativistic Breit–Wigner fit outside theintegration region.