The Higgs boson discovery at the Large Hadron Collider (LHC) completed the Standard Model of Particle Physics, and it confirmed the Higgs mechanism as a suitable description of the Electroweak- Symmetry-Breaking (EWSB). Nevertheless, the dynamics of the EWSB is still one of the most consequential questions in particle physics and a fascinating topic due to its connection to other open questions about the structure of the early universe, matter-anti-matter asymmetry and fermionic mass hierarchies. A pathway to study the EWSB mechanism is to investigate the longitudinal polarisation state of massive electroweak bosons. In this presentation, I will discuss the computation and phenomenology of higher-order QCD effects on polarised boson production cross-sections at the LHC and their impact on extracting the longitudinal polarisation fractions.