Inducing confessions, coercing confessions (for the police), and colluding confessions (for criminal suspects) are all illegal, and their testimony is invalid.
Even if there is no evidence of inducement or forced confession, in court, as long as the criminal suspect or witness states that the testimony was given under coercion, inducement, etc., and not out of true will, the prosecutor will not be able to provide a strong evidence. According to the principle of excusing the guilt beyond a reasonable doubt, most courts will not accept the prosecutor's evidence for the defendant. Therefore, in some cases, defendants and witnesses suddenly recanted their confessions, causing the procuratorate and the police to become passive.
Forced confessions are generally related to coercion, including the use of restrictions on personal freedom, threats and other means to force witnesses or criminal suspects to confess in accordance with the wishes of the police/prosecutor.