How to subscribe Youtube Channel in ios?

Question

I have tried with below URL

POST "https://www.googleapis.com/youtube/v3/subscriptions?part=snippet&fields=contentDetails,etag,id,kind,snippet,subscriberSnippet&key=(myClientId)&access_token=(myAccessTocken)

Request Body : {"snippet":{"resourceId":{"\(myChannelId)","kind":"youtube#channel"}}}

But fail to with Error code : 

"errors" : [
      {
        "domain" : "global",
        "reason" : "authError",
        "locationType" : "header",
        "location" : "Authorization",
        "message" : "Invalid Credentials"
      }