What's the difference between 注册 and 登记, both meaning "to register"? Typically I click 注册 = &quot;register&quot; to sign up for a new service on my phone.  However, 登记 also seems to mean &quot;register&quot; in a similar sense.  Searching on Jukuu.com:

法律不承认未登记的婚姻。
Marriage without registration is not recognized by law.
小学入学注册明天开始。
Elementary school enrolment begins tomorrow.

They seem similar, but I don't think they're interchangeable.  I'm not clear on this.
Question: What's the difference between 注册 and 登记?
(Note: The relevant question What are the differences between 报名，登记，挂号？ doesn't cover 注册)
注册 (register) can also mean "licensed" as in  "注册医生" (licensed doctor),  "注册执业" (licensed to practice) 

We don't say 登记医生 (registered doctor) or to 登记执业 (register to practice) 

When you 注册 on a system, you are officially registered/ enrolled or licensed

When you 登记 on a system, you are either officially registered/ enrolled or submitted an application