Is it possible to sue someone to recover money that was paid to him in exchange for completing a government transaction that he did not carry out and refused to return, and is this amount considered a bribe, bearing in mind that the person was an employee in the same government sector and then retired?

If an employee receives a salary for his work, it is not permissible to pay him money because it is a bribe, as the Prophet (peace and blessings of Allah be upon him) said: "Allah curses the one who offers a bribe, the one who takes it, and the intermediary between them." However, if the worker does not receive a salary, or if his work requires extra effort outside the scope of his job, then it is permissible to give him money. If an employee refuses to perform his work or delays it until he is paid money, then it is permissible to pay him; this is a bribe on his part but permissible for the payer. The employee must return the money he took unjustly, and if he does not, then his matter may be referred to the judiciary.