This preprint (not yet peer-reviewed) describes optical and spectroscopic follow-up of gravitational wave candidate S240413p, a binary black hole (BBH) merger event from LIGO-Virgo's O4 run with 98% classification confidence as a BBH. Researchers used the T80-South telescope via the S-PLUS Transient Extension Program (STEP) for multi-epoch imaging that covered the 99% credible localization region across approximately 300 days post-merger. The methodology prioritized galaxies hosting active galactic nuclei (AGN), identifying two optical transients (STEP2024gab/ZTF18acvgziq and STEP2024phe/ZTF19aaflhnr). Follow-up spectroscopy with SOAR/Goodman plus archival DESI spectra measured supermassive black hole masses in the hosts as log M_SMBH/M_sun = 7.15 ± 0.05 and 8.02 ± 0.04. The team then applied a thermal radiation-driven outflow model to predict flare delay times, finding migration traps at specific disk radii where mergers are theoretically more likely. No confirmed electromagnetic counterpart was found. This is a single-event study with inherent limitations: only one gravitational wave candidate was followed, a seasonal visibility gap could have hidden peak emission, the merger might not have occurred in the disk, or AGN variability might have obscured any signal. The work advances multi-messenger astronomy by testing the AGN channel for BBH mergers, a pathway distinct from isolated binary evolution in the field. It connects to earlier theoretical work such as McKernan et al. (2018, arXiv:1702.07818), which modeled how AGN disks can catalyze rapid BBH mergers through migration traps, and a 2021 study by Graham et al. on potential optical flares from mergers embedded in disks (arXiv:2101.01289). Previous media coverage of similar events often emphasized prompt emission searches within hours or days, missing the key insight here: predicted delays can stretch to hundreds of days, aligning precisely with the late-epoch observations near migration trap locations (R_BH/R_g ≈ 10^4.2 and 10^3.4). What the original abstract underplays is the strategic implication for the Rubin/LSST era - generic wide-field surveys may miss these signals without AGN-prioritized, physically motivated long-baseline monitoring. Synthesizing the sources reveals a pattern: while neutron star mergers like GW170817 produced clear kilonovae, BBH events require dense gas environments like AGN disks to generate detectable light, yet confirming this channel remains elusive due to timing mismatches and background noise. This non-detection refines rather than refutes the AGN-merger hypothesis and underscores the need for coordinated, patient follow-up campaigns.