The Access Token provided to the Twilio API is not yet valid.
Twilio Access Tokens are generated with a nbf field that determines the start of the token's lifetime. Normally this is set to the current time when the token is generated; check whether your computer's clock has drifted.
To check whether the Access Token is structurally correct, you can use the tools available at jwt.io.
For the details of Twilio's specific Access Token implementation and the requirements of the issuer and subject fields, see the documentation.