Is working in a mixed-gender sports club – despite dealing only with men and seeing women – unlawful (haram), and is the money earned from it unlawful (haram)?

The criterion for prohibited intermingling (ikhtilat) is the gathering of men and women in one place without adherence to Islamic guidelines. It is not permissible to work in a place that fits this description. However, the presence of a disapproved act (munkar) in the workplace, such as intermingling, does not make the money earned from it unlawful. If the employee's work itself is permissible, then their salary is permissible.