1 John 5:16 -
If anyone sees his brother sinning, if the sin is not deadly, he should pray to God and he will give him life. This is only for those whose sin is not deadly. There is such a thing as deadly sin, about which I do not say that you should pray.
If we pray for someone else, who is involved in venial sins, then our prayers will aid that person, even having those sins forgiven. “Give him Life” means God’s Graces will be given to that person - God is “Life Eternal” and His Graces are what we refer to when Jesus gives us Eternal Life.
If someone is in a state of mortal sin, none of our prayers can enable this sin to be forgiven. That person has to repent, confess, and do penance.
It does seem to be misleading, because we should pray for that person’s conversion, but our prayers won’t directly get their sin forgiven.
All of this, of course, comes from the “Gospel of Notworthy” and is simply my opinion.