Is the money my friend takes for mediating between two companies permissible?

It is permissible for an employee to receive a brokerage commission from a foreign company or from their employer, or from both, if the brokerage is not part of their official duties and they perform it outside of working hours, provided it is in the form of advice and free from fraud or favoritism. However, if it is part of their work or during working hours, then their company's permission is required for them to legitimately take a commission from the other company. A number of the Tabi'un have permitted brokerage.