Channel subscriber count of a channel is not increasing if I subscribe to that channel by youtube API

Question

I am using youtube API to subscribe a youtube channel. I am using access token for calling API. The API call is successful and if I go to that channel it is showing subscribed. But the subscriber count is not increasing even after 10 days. If I subscribe manually then the count is increasing. I tested this with my two youtube channels. Is there any difference between subscribing by API and manually. How can I achieve the same by API call i.e. increase in count when subscribe through API.