Is it safe to post a negative review about a company in Indonesia?

Post what you can evidence, and frame it as your own experience. Indonesia's Electronic Information and Transactions Law has been used against consumers who posted complaints online — the Prita Mulyasari case is the standing precedent — so accuracy is your protection rather than a limitation. Stick to dated facts, amounts, and documents you actually hold. Describe your own experience as your own experience. Do not state as settled fact something you cannot evidence. Keep the originals. A precise, sourced account is both safer and considerably more damaging to a company than an insult, because it cannot be dismissed as an emotional outburst.