The Didache or the teachings is a very old letter written by the Apostles in the first century. By the early Church this letter was certainly recognised, But when the list (in the fourth century) with canonical and apocryphal letters are recognised for publication the Didache aren’t included in the Bible.
You will find also the word Didache or teaching in the textus receptus (Bible)
(about teaching the truth , 45 times )
The Greek word didache did-akh-ay’
means ” instructions of the act “
Matthew 7:28-29 And it became, when the Jezus finishes the sayings ( logos ),that the throngs were astonished on His teaching (Didache ). For He was teaching them as one having authority and not as the scribes.
Translations by ScrTR ● Greek New Testament Scriveners Textus Receptus 1894