You need to be logged in to be able to send participation requests. For some events, the creator can specify requirements that individuals who wish to participate must meet (e.g., minimum age, location, etc.). You can only request to participate if you meet these requirements. Additionally, an event can be (temporarily) paused, during which no (further) participation requests are possible.
If you accept a participation request, the person will be notified of the acceptance, granted access to the event chat, and shown further details about the event (location, time). If you decline a participation request, the person will be notified within seven days. If you do not respond to a participation request within seven days, it will be automatically declined.