Calling the Authentication APIs allows you to get and verify bearer tokens returned by Cashfree. Cashfree require these token for all further communication.

Cashfree libraries automatically call the Authorize API and internally store the token.
Do not store the token in an insecure manner. Regenerating a new token does not invalidate the already generated token. Token generated from one IP address cannot be used from a different IP.
Token generated is valid for 600 seconds. Please ensure that you recall the authorize API once the token has expired.

Ensure your IP is whitelisted. To find out how to whitelist your IP or if you have a dynamic IP, take a look here).