Does the "Kiến Phúc Thông Bảo" coin exist?
建福通寶

Mai Ngọc Phát, Bùi Tiến Đạt, Vietnam Numismatics #1 (10-2017), p28-32

Historical background

In the sixth month of the year Quí Mùi [癸未] (July 19, 1883), King Tự Đức passed away. Because the king had no descendants, he previously adopted three nephews, Nguyễn Phúc Ưng Ái (changed his name to Ưng Chân in 1869), Nguyễn Phúc Ưng Kỷ, and Nguyễn Phúc Ưng Đăng. During this time, Vietnam fell into a period of extremely severe political crisis, with power falling into the hands of mandarins. The territory gradually diminished under the occupation of the French, as evidenced by the Harmand (1883) and Patenôtre (1884) treaties, which completely ended Vietnam's status as an independent nation under the Nguyễn dynasty. Before Kiến Phúc ascended the throne, there were two other kings who were brought to power and dethroned within a very short period: King Dục Đức [育德] (Nguyễn Phúc Ưng Chân) ruled for 3 days, and King Hiệp Hòa [協和] (Nguyễn Phúc Hồng Dật) held the throne for 4 months.