According to the History of Ming, in 1412 (i.e., some time between the third and fourth voyages of Zheng He's fleet), Hong Bao was sent by the Yongle Emperor as the envoy to Thailand.
According to the inscription, the two Principal Envoys (正使) sent by the Xuande Emperor to the countries of the Western Ocean were the eunuchs Zheng He and Wang Jinghong.
Hong Bao was one of the five Assistant Envoys (副使) (along with Zhu Liang, Zhou Man, Yang Zhen, and Zhang Da).
Hong Bao, as well as all other Principal and Assistant Envoys except for Zhang Da, had the eunuch rank of Grand Director (太監, Taijian).
According to Edward L. Dreyer's analysis of the preserved sources about the voyage, in particular Ma Huan's book, Hong Bao commanded a squadron which most likely separated from the main fleet in Semudera in northern Sumatra (although other suggested it may have happened earlier, in Qui Nhon in Champa), and visited Bengal.