Trading itself is legal, but the bonus situation for licensed brokers is restrictive. BAPPEBTI rules do not permit the deposit matches, no-deposit credit and aggressive welcome bonuses that international brokers build their marketing around. A broker that is properly licensed in Indonesia is generally not allowed to lure clients with those incentives, so if you trade with a compliant local broker you should not expect them.
That gap is exactly why offshore brokers target Indonesian traders so heavily. They can dangle the bonuses that licensed firms cannot, but they do so from outside BAPPEBTI oversight. Choosing one means trading with a broker that is not authorised to serve Indonesian residents and is not bound by the local rules on client fund handling, leverage or dispute resolution.
So the honest position is that the most attractive bonuses available to Indonesians come from brokers operating outside the licensed system. You can still trade legally and safely with a BAPPEBTI-licensed broker, you just trade for the conditions and protection rather than for a promotion. Verify any broker against the BAPPEBTI register before depositing.