John 16:9 New English Translation

⁹concerning sin, because^[a] they do not believe in me;^[b]

John 16:9 tn Or “that.” It is very difficult to determine whether ὅτι (hoti; 3 times in 16:9, 10, 11) should be understood as causal or appositional/explanatory: Brown and Bultmann favor appositional or explanatory, while Barrett and Morris prefer a causal sense. A causal idea is preferable here, since it also fits the parallel statements in vv. 10-11 better than an appositional or explanatory use would. In this case Jesus is stating in each instance the reason why the world is proven guilty or wrong by the Spirit-Paraclete.
John 16:9 sn Here (v. 9) the world is proven guilty concerning sin, and the reason given is their refusal to believe in Jesus. In 3:19 the effect of Jesus coming into the world as the Light of the world was to provoke judgment, by forcing people to choose up sides for or against him, and they chose darkness rather than light. In 12:37, at the very end of Jesus’ public ministry in John’s Gospel, people were still refusing to believe in him.

New English Translation (NET)