Teachers often immediately accept your lessons request, but there are some situations where your request is unsuccessful.
For example, if your teacher received multiple Instant Tutoring requests from many students at the same time. Teachers can only accept one request from one student. Once a teacher accepts a request from a student, all other requests are automatically declined.
If your request is unsuccessful, try making another Instant Tutoring request with another teacher offering Instant Tutoring. There are always new teachers from all over the world that will "turn on" their Instant Tutoring Availability.