The primary outcome is whether the participant has taken up our HIVST-online service during a 6-month follow-up period. This behavioral outcome is recorded by us objectively. Among those who had not taken up HIVST at Month 6, they will be contacted by phone/social media to ask several brief questions to assess secondary outcomes, which include: 1) whether having taken up any form of HIV testing other than HIVST-online and 2) intention to take up HIVST-online or other forms of HIV testing in the next six months.