Involved in the production of blood-red nectar containing the alkaloid nesocodin and that serves as a visual attractant for pollinator visitation, including vertebrates such as Phelsuma geckos (PubMed:35074876). The nectar is initially acidic and pale yellow, but slowly becomes alkaline before turning into red within 24 hours (PubMed:35074876). Together with NEC1 and NEC2, facilitates the condensation of sinapaldehyde ((E)-3,5-dimethoxy-4-hydroxycinnamaldehyde) and proline to form nesocodin, a pigment with a stable imine bond (PubMed:35074876). Catalyzes the conversion of sinapyl alcohol to sinapaldehyde (PubMed:35074876). (E)-sinapyl alcohol + O2 = (E)-sinapaldehyde + H2O2 Alkaloid biosynthesis. Monomer. Confined to nectaries. Belongs to the GMC oxidoreductase family.