Is overtime pay considered permissible (halal) or forbidden (haram) if the work is done during official working hours and with the approval of the supervisor to perform additional tasks?

If the additional work is carried out in coordination with the authorized official, there is no harm in taking payment for it. This is because a private employee is not obligated to perform tasks exceeding their official working hours except by stipulation or custom. Analogous to this is what jurists mentioned regarding a shepherd, who is not obligated to tend to newborn animals except by custom or stipulation.