What does Jeremiah 29:31 mean?

Send this message to all the exiles: ‘This is what the Lord says about Shemaiah the Nehelamite: Because Shemaiah has prophesied to you, even though I didn’t send him, and has made you trust a lie—’ Jeremiah 29:31 - Modern Text Bible

(God tells Jeremiah to warn the exiles about Shemaiah’s lies and the danger of trusting him.)