Our observer frame spectrum of an AT2017gfo-like KN, computed at three distinct time points with an assumed luminosity distance of 40 Mpc and a viewing angle of 25 degrees. The left panel displays the spectrum before applying any correction, while the right panel illustrates the spectrum after applying the flux correction as detailed in Eq. A.4. A comparison with the AT2017gfo observational data, see for example Villar et al. 2017, reveals that the u filter emission (3694 Å) is initially too high. After implementing the correction, the emission aligns more closely with the observational data.