This is an interesting report, since there is no actual deal, simply the alleged offer. The purpose seems to be to imply that he is flipping on Trump.
Via Daily Caller:
Donald Trump’s former National Security Advisor Mike Flynn reportedly told federal investigators that he is willing to testify on President Trump’s potential connections to Russia in exchange for full immunity.
Flynn resigned after it was revealed that he met with Russian ambassador to the United States Sergey Kislyak during the 2016 election and subsequently lied about it.
Officials close to the situation told The Wall Street Journal that Flynn made offers to both the FBI and Senate Intelligence Committee staffers, yet neither party has accepted.