Fasiq is a person who commits sins openly and don’t obey the commands of Allah (swt).
Fajir means a person who careless and also doesn’t have faith that why in Qur’an Kafir and Fajir have mentioned together.
أُولَٰئِكَ هُمُ الْكَفَرَةُ الْفَجَرَةُ
These are they who are unbelievers, the wicked.(80:42)