Wrong fixed parameters . If you fix a line wavelength outside your plot, it will NOT be taken into account. Wrong baseline . If you fit a baseline without selecting baseline parts, the whole spectra is used which may give unusable baseline for faint lines. It is not possible for the moment to fit correctly nor simply a faint line merged with noise or fringes.
Baseline fit is constant.
Baseline fit is linear. Baseline fit is a 2 degree polynomial. Baseline fit is a 3 degree polynomial. For non-composite fits, these parameters are set to zero. Note that this method does not allow the baseline fit and line fit together as in Gaussian method.