Error when trying to register

I'm getting a "The event you are trying to register is not found" error when trying to register for an event. What should I look for? It's a child event, the parent event doesn't give this error.

Hello Lucy

It could cause by something wrong with Alias of the event. For this, go to Events Booking -> Configuration, look at SEF Router Settings tab, set Insert Event ID config option to Yes, then check it again. The error should be gone

Regards,

Tuan