Is it permissible for an employee to take the remaining amount from a pre-paid accommodation invoice, knowing that the actual cost of the accommodation is less than the amount disbursed, and that both the direct manager and the manager above him have authorized this?

If the contracting company stipulates an invoice from the hotel stating that the employee resided there and paid 30 dinars, then it is not permissible to reside outside the hotel and submit an untrue invoice, due to the falsehood and forgery involved. The difference in cost is not permissible for you, and the managers' approval does not change the ruling whatsoever. The decisive factor is the approval of the paying company, which allocated accommodation in a specific hotel in exchange for proof of that. Therefore, it is not permissible to deceive it and take its money unjustly. So, either you stay in the hotel and bring the invoice, or you stay outside, and it is not permissible for you to provide a false invoice, nor is it permissible for the hotel employee to issue one.