What is the ruling on taking a symbolic commission from a shipping company if its prices are lower and the offer was presented to the manager, who approved it, without informing him of the commission, given that the salary is insufficient for living in that country?

If your job is to search for and negotiate with shipping companies, then it is not permissible for you to take a commission from the shipping company without the permission of your employer. This permission is not waived due to a low salary. However, if that is not part of your obligatory work, then there is no harm in you taking the commission.