The government's whole case against Carter Page and Team Trump rated on the Steele Dossier. So, in early October of 2016 a team from the FBI and the Department of Justice flew to London to interview Steele, a former British spy. Steele told them he couldn't corroborate anything in the dossier. He said he relied on a primary source who had a network of sub-sources. When the FBI asked who the primary source was, Steele refused to reveal the person's identity. But the FBI figured it out and interviewed the main source in January 2017.
During 3 days of interviews at the FBI's Washington field office, the primary source, Igor Danchenko, told the FBI that the dossier was just hearsay, misstatements and exaggerations. The source told the FBI that he couldn't corroborate anything in the dossier.
President Trump was sworn into office on January 20th, 2017. Danchenko was interviewed on January 24, 25 and 26th. So, at the end of President Trump's first week in office, the FBI knew its case had crumbled. Did they tell the FISA Court? Did they stop the spying? No.