Top panel: Median K-band spectrum for GRAVITY+ (grey) with a median S/N of ≈180. Its best-fit retrieval, including ¹³CO, is shown in pink, and the retrieval without ¹³CO is shown in black. The inset shows a zoom-in on the 2.34–2.40 μm region. Bottom panel: Residuals between the data and each model, respectively. The retrieval inflates the error bars in order to find the best-fit model, resulting in residuals not explained by the model.