It depends on the cannabis club. Only the clubs listed on this website will allow you to approach without the invitation, but is always polite to either request one on this website or to contact them directly on their website prior your arrival. The most common reply for a cannabis club making new members is:
“Please, show this message at the reception desk and bring your ID to identify yourself as a legal adult (age). We can’t answer further questions till we meet face to face at the club.”
If you go to a cannabis club that is not listed on this website you are most likely to be rejected.