The legal position needs stating precisely. Operating or brokering forex trading from inside Vietnam without a licence is illegal, and no such licences are issued; the SBV and police continue to shut down unauthorized trading floors and money-changing points. For an individual using personal funds with a foreign broker, there is no explicit ban, but there is also no authorization and no recognition, which is what a gray zone means: prosecutions have concentrated on operators, promoters and fraud schemes, not on retail traders, and that is an enforcement pattern, not a guarantee.
No domestic regulator approves or restricts promotions, so the bonuses Vietnamese traders see are the offshore brokers' standard global offers, applied wherever those brokers' own eligibility lists allow. Every account is held abroad, every protection comes from the foreign licence, and no Vietnamese authority will mediate a dispute.
Funding reflects the controls: the dong is not freely convertible, direct wires to foreign brokers are impractical for most people, and the common rails run through crypto on-ramps and local e-wallets. That adds counterparty steps between you and the broker, which argues for small amounts, early withdrawal tests, and skepticism toward any bonus that requires locking a large balance.