Metallicity (left) and C/O (right) distribution calculated from the posterior distributions of the cloudy+CO prior retrieval. The black solid lines indicate the median, and the dashed lines depict the ±34.1% confidence regions. The dotted line shows the 3σ upper limit of 0.454 for C/O. The same calculations without a tight CO prior yielded a very sub-solar metallicity of [M/H] = $-{1.35}_{-0.73}^{+1.25}$ and a very low C/O of ${1.33}_{-0.70}^{+4.79}$ · 10⁻³ (see Sect. 4.5).