Higgs pair production processes provide the direct probe to the Higgs boson self-coupling ($\lambda_{3}$). However, as well known such a processes have a small production cross section. It is also known that single Higgs processes indirectly depends on $\lambda_{3}$, thus an alternative method to measure the $\lambda_{3}$ is considering $\lambda_{3}$-dependent next-to-leading-order (NLO) electroweak (EW) corrections in single Higgs processes. The magnitude of these corrections are encoded by some process and kinematic-dependent coefficients named as $C_{1}$. In the following, an overview of the determination and parametrization of the $C_{1}$ coefficients in Simplified Template Cross Sections (STXS) bins performed by ATLAS and CMS is shown in connection to the latest H+HH combination results with full Run 2 dataset.