I send query

https://accounts.zoho.com/oauth/v2/token? refresh_token={refresh_token}&client_id={client_id}&client_secret={client_secret}&grant_type=refresh_token

like this described in  https://www.zoho.com/crm/help/api/v2/#refreshing-tokens

And get answer

( [access_token] => 1000.3e3ff587727bf933********689d55dd.5b5a3456********75cb22a32b5e783 [expires_in_sec] => 3600
[api_domain] => https://www.zohoapis.com
[token_type] => Bearer
[expires_in] => 3600000 ) 

*I replace some characters in access_token with stars

Why access_token format os so strange? Why API give me 401 error (access denied) if I try use this token? I separate token with point delimiter and tried use both keys, but no one works.