AKA Teachings of the Twelve makes references to a written Gospel, possibly predating Epistles of Ignatius (A.D. 115)'s historical indicator that the Gospels and Pauline letters were accepted as Scripture and were circulating throughout the Church.
(The Origin of the Bible: Newly Updated by F. F. Bruce, J. I. Packer, Philip W. Comfort, and Carl F. H. Henry, 2020. The Canon of the New Testament by Milton C. Fisher, Pages 68-72.)
By the early 4th century, the Didache was classified as spurious.
(The Origin of the Bible: Newly Updated by F. F. Bruce, J. I. Packer, Philip W. Comfort, and Carl F. H. Henry, 2020. The Canon of the New Testament by Milton C. Fisher, Page 74.)