Is it permissible to spend the financial amounts obtained from assignments outside the city, knowing that I did not go on these assignments, but rather remained at my work to complete other tasks at the request of the manager?

It is impermissible to receive money for tasks that have not been performed, as this involves lying and consuming people's wealth unjustly, according to the Almighty's saying: "And do not consume your properties among yourselves through falsehood." This includes taking wages for work whose obligations have not been fulfilled. If the manager is in need of an employee, he can request a salary increase or a financial bonus for him.