<![CDATA[ABSTRACT; This article aims to analyze whether the unilateral freezing of a seller's account by an online marketplace operator can be qualified as default (wanprestasi) and to determine the limits of freedom of contract in the standard-form agreement between the two parties. The issue is urgent because marketplace operators routinely reserve broad discretion to suspend accounts and withhold sales proceeds, while sellers, particularly micro and small businesses, depend economically on the platform and have virtually no bargaining position. This normative juridical research uses statute and conceptual approaches, drawing on the Indonesian Civil Code, the Electronic Information and Transactions Law, Government Regulations No. 71 of 2019 and No. 80 of 2019, and the relevant scholarship. The analysis shows that the relationship is a valid standard-form electronic contract under Article 1320 of the Civil Code, yet the operator's discretionary power is limited by good faith (Articles 1338(3) and 1339), the requirement of a lawful cause, and the procedural duties of electronic system operators. A freeze constitutes default when it is not grounded in the agreed reasons, is not preceded by notice and an opportunity to clarify, is protracted beyond the promised period, or is disproportionate, especially when sales proceeds are withheld. A freeze based on a legitimate ground and a fair procedure is not default. Sellers may pursue a default claim, an unlawful-act claim, or simplified lawsuit procedures]]>
