For most short-term visas, including the Visa on Arrival (VOA) and various visit visas, Indonesian immigration authorities require proof of onward travel, such as a return or onward ticket. This is a mandatory document for visa issuance and is usually checked during both the application process and at border entry points.
The main exception is for holders of long-term residence visas, such as KITAS or KITAP, where a return ticket is not required. If you plan to stay in Indonesia for an extended period on a social visa or are traveling around Asia without a fixed return date, there are workarounds. Some travelers purchase a refundable ticket or a low-cost onward ticket to another country to satisfy this requirement.
While it is possible to enter Indonesia with a one-way ticket in certain cases, be prepared to show proof of onward travel if requested by immigration officials. Failing to provide this can result in denied boarding at your departure airport or refusal of entry upon arrival.