In the last decade, measurements of $b \to s \mu^+ \mu^-$ processes have shown intriguing discrepancies with respect to the Standard Model (SM) predictions. In particular, analyses of $B^0 \to K^{*0} \mu^+ \mu^-$ decays reported tantalising deviations in one of the angular observables of the decay, namely $P_5^\prime$. Nonetheless, our current understanding of the hadronic uncertainties associated to the SM predictions limits our ability to interpret these results as signs of physics beyond the SM. It is therefore crucial to find reliable ways to quantify the impact of these uncertainties on the decay observables. In this seminar, we present the results of the first $q^2$-unbinned amplitude analysis of $B^0 \to K^{*0} \mu^+ \mu^-$ decays, where $q^2$ is $\mu^+\mu^-$ the invariant-mass squared, based on data collected by the LHCb experiment corresponding to an integrated luminosity of $4.7\,{\rm fb}^{-1}$ . For the first time, Wilson coefficients and local and non-local hadronic contributions are determined directly from the unbinned data using a model dependent approach. By exploiting the $q^2$ dependence of the decay, a precise characterisation of the impact of non-local hadronic effects on the decay observables is achieved. This new study provides the most accurate investigation of the $B^0 \to K^{*0} \mu^+ \mu^-$ decay process to date.

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