This research is based on the principle that online sales and purchase agreements are regulated by Article 1320 of the Indonesian Civil Code, which outlines the essential elements for a valid agreement: mutual consent, legal capacity, a specific object, and a lawful cause. The study also highlights the challenges faced by e-commerce businesses in cash on delivery (COD) transactions, where buyers may act irresponsibly by refusing to accept or pay for the goods they have ordered. This behaviour creates legal and financial uncertainty for business actors. This research refers to several legal instruments, including the Civil Code, Law No. 8 of 1999 on Consumer Protection, and Law No. 11 of 2008 concerning Electronic Information and Transactions, as amended by Law No. 19 of 2016. The objective of the thesis is to analyse the legal responsibilities of consumers in COD transactions and to explore the available legal protections for online sellers. A qualitative method with a normative-empirical legal approach is used to examine both legal norms and their application in practice. Although the transactions take place through digital platforms, the legal validity of such agreements remains equal to that of conventional sales contracts. The primary difference lies in the medium used, not in the legal force of the transaction