If you are working as an entrepreneur/freelancer/ZZP-er, you are allowed to do this in addition to your studies without needing a work permit. It is possible for all international students to do self-employed work for an unlimited amount of hours, in addition to their studies and part-time jobs. These self-employed students need to be registered with the Chamber of Commerce.
To register as a ZZP-er/freelancer you need to register at the Dutch Chamber of Commerce(opens in a new tab) (Kamer van Koophandel or KvK). The most common legal structure used by freelancers in the Netherlands is the eenmanszaak (sole trader or one-person business). You first need to complete the eenmanszaak form on the KvK website. Forms for all legal structures are available in both English and Dutch. Once your form is complete, schedule an appointment to visit your local KvK via the appointment page(opens in a new tab).
While registering with the KvK, you should also ask to be registered with the Belastingdienst(opens in a new tab) (Dutch tax office), which will issue you with a BTW number (VAT number(opens in a new tab)). The Dutch tax office collects tax on all products and services sold in the Netherlands. They do this by requiring all businesses to add BTW tax (usually 21 percent) to their sales. The tax office then collects this tax four times a year via the VAT declaration (BTW aangifte). If you have a freelance business then you will also be collecting for the tax office. If your business earns under €20,000 a year then you can register for KOR (small business scheme), this means you do not have to charge VAT to your customers and no longer have to file a quarterly VAT return (however this means you will also no longer be able to claim/file VAT on your business expenses). You can read more about this scheme here(opens in a new tab). Important note: if you register for this scheme you can only deregister after three years, or if your turnover exceeds €20,000 in one year.
BTW/VAT can be pretty complicated, and it is advised to get an accountant/bookkeeper to help you out with the process. Some recommended places are:
You can find out more about how BTW/VAT works in the Netherlands here(opens in a new tab).