If you are staying in Japan for example, under a Student visa, you must receive permission for activities other than that permitted under the current status to make money. Even if you are already making money under a certain working visa, you also need to receive permission for activities other than that permitted under the current status if you wish to engage in activities permitted under your status.
A certain American pastor in Japan has received permission for activities other than that permitted under the current status since he needs to make money outside the church he serves at.
It is relatively easy for international students to receive permission for activities other than that permitted under the current status since they do not need consent of anyone, but if you have a working visa, you need to be careful since you can not get permission freely.
Most applicants of permission know requirements such as working for 28 hours or less per week and no activities such as adult entertainment business, store-based special sexual entertainment business, specific entertainment restaurant businesses conduct, activities conducted in the course of non-store-based special sexual entertainment business, video transmission-based special sexual entertainment business, store-based telephone dating business, or non-store-based telephone dating business. But also,if a person is engaged in activities that fall under the status of residence based on a contract with a public or private organization in Japan, the organization must agree to the person engaging in activities outside the status of residence.
If you have a working visa and receive permission for activities other than that permitted under the current status without a consent of your organization, your employer might refuse to provide necessary documents when you need to renew your visa. Please heed.