How will i get the authorization token?

How will i get the authorization token?

I am using PHP SDK to connect to ZOHO. Go insert leads for the company profile. I followed up procedure as in " https://www.zoho.com/crm/help/developer/server-side-sdks/php.html". I get grant token, access token and refresh token too. But Unable to get any authtoken. It's giving null. With this " $oAuthTokens = $oAuthClient->generateAccessTokenFromRefreshToken($refreshToken,$userIdentifier);".

Is there any way i can get that.