Charles Ellicott Commentary Jeremiah 29:8

"For thus saith Jehovah of hosts, the God of Israel: Let not your prophets that are in the midst of you, and your diviners, deceive you; neither hearken ye to your dreams which ye cause to be dreamed." — Jeremiah 29:8 (ASV)

Let not your prophets and your diviners ... —These words are significant, showing that the same agencies counteracting the prophet’s teaching in Jerusalem were also at work in Babylon.

There, too, “prophets and diviners,” whom the Lord had not sent, were prophesying a speedy deliverance. It was therefore necessary to reiterate to those who would listen to the prophet’s warnings that the exile would run its appointed seventy-year course, as Jeremiah had announced to the people of Jerusalem (Jeremiah 25:12; Jeremiah 27:22).

The phrase dreams which you cause to be dreamed (an altogether exceptional phrase) indicates that the supply of such visions was created by the demand for them.