Is it permissible to accept a housing allowance verbally agreed upon with a contracting company, if a per diem allowance is already being disbursed by the Human Resources Department for the same mission?

If the department manager is authorized to stipulate a housing allowance for employees, then there is no harm in benefiting from it. However, if he is not authorized, and the secondment allowance includes a housing allowance, then the employee relations department must be informed so that the amount equivalent to the housing can be deducted or granted to you. In any case, there is no harm in benefiting from the housing allowance disbursed by the contracting company.