Spectra containing the PO lines in the GUAPOS observations. Upper panel: spectrum extracted towards region 1. The red curve indicates the PO lines fitted according to the best-fit parameters in Table 2 (assuming T_ex=26 K). The horizontal red dashed line corresponds to the 3σ rms level. Lower panel: same as top panel for region 2, using the fit shown in Table 2, where T_ex=12 K is assumed. The observed spectra at the original frequency resolution are shown in light grey, while the spectra smoothed by a factor of 2 are shown in dark grey.