This study systematically reviews how BNPL ecosystem design interacts with information asymmetry and behavioral biases to produce what this review conceptualizes as “ghost debt,” an author-developed construct distinguished from related notions—debt opacity, hidden debt, over-indebtedness, debt stacking, financial fragility, repayment burden, and credit invisibility. Following PRISMA 2020 guidelines, a Boolean search (“buy now pay later” OR “BNPL”) was run in Scopus (TITLE-ABS-KEY field; English-language, peer-reviewed journal articles, 2010–2026) for studies addressing BNPL design, consumer decision-making, debt opacity, or financial vulnerability. Of 179 records screened, 26 studies passed dual-reviewer title/abstract and full-text screening and were retained for extraction and synthesis; additional theoretical and contextual literature was used only to interpret findings. The synthesis shows that ghost debt emerges from BNPL design features—such as installment framing that lowers total-cost salience—compounded by channel-shifting practices (e.g., BNPL-on-card) and limited credit-bureau reporting; these mechanisms disproportionately push liquidity-constrained consumers toward downstream financial distress, including overdrafts and debt stacking. This review’s principal contribution is conceptualizing ghost debt as a systemic outcome cascade integrating information-asymmetry theory, behavioral decision theory, embedded-finance infrastructure, and fragmented credit reporting, explaining how low-friction digital credit obscures cumulative financial obligations. Mitigating ghost debt requires transparency-by-design interventions—standardized point-of-sale disclosures, consumer obligation dashboards, and open-banking-enabled debt aggregation—paired with stronger regulatory oversight and integrated credit reporting, protecting financially vulnerable groups from invisible debt traps while preserving BNPL's utility for cash-flow smoothing.