The coupling of the electroweak gauge bosons in the Standard Model is lepton flavour universal. Rare semileptonic $b\to s\ell^+\ell^-$ decays constitute sensitive probes for New Physics models that violate lepton flavour universality. Of particular interest are measurements of the branching fraction ratios $R_{K^{(*)}}={\cal B}(B\to K^{(*)}\mu^+\mu^-)/{\cal B}(B\to K^{(*)} e^+e^-)$ which show some tension with the precise SM predictions. These proceedings summarise the latest results from the LHCb experiment on lepton flavour universality tests in rare $b\to s\ell^+\ell^-$ decays.