Comparisons between our model spectra (blue) and observations (black). The observed spectra have been rebinned by a factor of 10 (using SPECTRES, Carnall 2017). Panel A: Comparison of the +0.9 d X-shooter spectrum with our best-fitting TARDIS model. Panel B: Comparison of the early FORS2 spectrum (+0.9 d), and our best-fitting TARDIS model. Panel C: Comparison of the two later OSIRIS spectra (+6.5 and +8.4 d) with their corresponding TARDIS models. The +6.5 d spectrum and model have been offset by 3 × 10⁻¹⁷ erg s⁻¹ cm⁻² Å⁻¹, for clarity. Panel D: Comparison of the late-time GMOS spectrum (+15.6 d), and its corresponding TARDIS model. The vertical shaded bands in panels B, C and D correspond to regions of absorption in the observed spectra. The species dominating these same absorption features in our best-fitting TARDIS models have added to the top of each band in panel B.