Is it permissible to accept a financial bonus offered by the company manager, when he submits it to the financial department as an invoice for purchases or equipment, because there is no financial item for incentives, and he claims that he has a monthly financial allowance that he can dispose of freely?

If the manager is authorized by the owner to allocate bonuses to diligent employees, there is no objection to benefiting from the bonus he grants. How he raises the matter to financial management is his concern, and the employee has nothing to do with it. The important thing is that the manager has the authority to grant the bonus; otherwise, it is not permissible to take it.