What is the ruling on someone working for a company that reduces invoice values to evade customs, given that the state does not apply Sharia and is considered to be imposing illegal taxes (maks)?

The ruling on this person's action concerning the aforementioned discount depends on the ruling on evasion. If evasion is permissible, then assisting in it and working on everything related to it is permissible. If evasion is prohibited, then assistance and work aiding it are prohibited. If he does not directly engage in or assist in something forbidden, then there is no blame on him, because he receives wages for permissible work.