In the Netherlands, purified psilocybin is illegal except in approved research. The legal route is to use magic truffles, which contain psilocybin/psilocin and are lawful to possess. What is often called psilocybin therapy is therefore offered as guided truffle sessions.
To stay within the law, book with a Dutch provider who uses legally obtained truffles, keeps sessions in the Netherlands, and presents the work as coaching or wellness rather than medical treatment. Do not buy or handle isolated psilocybin, do not extract compounds, and do not transport truffles across borders.
Typical steps include an intake for suitability, preparation guidance, a supervised session with legal truffles, and integration afterward. Arrange a safe setting, avoid driving until fully sober, and follow local rules set by the provider and venue.
For an example of how truffle-based sessions are organized in the Netherlands, see this overview. I hope this clarifies the legal path.