This schematic illustrates the trial arms from the perspective of a participant. In the standard-of-care arm, the participant was offered a test at a standard price (US$22). In the pay-it-forward arm, the participant was offered a free test, told that previous men donated to make this test possible, and shown postcards written by these previous men (“caring”). Then, the participant was asked whether they would donate toward testing for prospective patients (“voluntary donation”). In the pay-what-you-want arm, the participant was offered a free test. Then, the participant was told that they could pay any desired amount for their own test (“voluntary payment”). STD=sexually transmitted disease.