SMS confirmation not sent after user registration

I have a strange error (using Clickatell).

If I assign a phonenumber to an existing user, the sms is sent

But if I try to register as a new user - registering my phonenumber to get confirmation code, I do not recieve a sms.

There is neither any problem using "Send to phone".

We are going to use sms-authorization, so it's crucial for us to be able to send out passwords to new users on SMS.