Sins committed by one person against another person
“God’s forgiveness, however extensive, only encompasses those sins which man commits directly against Him, “bein adam la-Makom“; Those sins in which an injury is caused to one’s fellow man, “bein adam le-ḥavero” are not forgiven until the injured party has himself forgiven the perpetrator.
Hence the custom of seeking forgiveness from those one may have wronged on the eve of Yom Kippur, without which proper atonement cannot be made …
The law regarding physical injury, for example, is explicit in that even after the various compensatory payments have been made, the inflicter of the damage must seek the forgiveness of the injured party for the suffering caused (BK 92a; Yad, Ḥovel u-Mazzik 5:9; Sh. Ar., ḤM, 422).”
https://merrimackvalleyhavurah.wordpress.com/ethics/forgiveness/