Albert Barnes Commentary 2 Chronicles 33:18

"Now the rest of the acts of Manasseh, and his prayer unto his God, and the words of the seers that spake to him in the name of Jehovah, the God of Israel, behold, they are written among the acts of the kings of Israel." — 2 Chronicles 33:18 (ASV)

The “prayer of Manasseh,” preserved for us in some manuscripts of the Septuagint, has no claim to be considered the genuine utterance of the Jewish king. It is the composition of a Hellenistic Jew, well acquainted with the Septuagint, writing at a time probably not much before the Christian era.

The words of the seers who spoke to him - See 2 Kings 21:11–15.

The writer of Chronicles usually speaks of “the book of the kings of Judah and Israel” (or “Israel and Judah”). Here he designates the same compilation by a shorter title, without (apparently) any special reason for the change. Compare 2 Chronicles 20:34.