How to check the availability of a number in the VIBER messenger?

Question

PHP

Hello. I came across the Viber messenger API, the API is quite functional, but 1 moment is not clear. Is it possible to somehow check if this phone is in Viber, I personally did not understand how to do this. Everything is based on Viber user_id and it is impossible to search by phone without knowing the user_id, but I don’t know it. Has anyone else experienced this, how can I get out?