By default, the class stores tokens in session variables.
If you come in another day after having closed your browser, the original session is gone, so it is not possible to recover the original token.
To preserve tokens for a longer time, you need to use the mysqli_oauth_client.php or something similar that stores tokens in a database.
If you are storing the access token by yourself in a database, keep in mind that you also need to save and restore the expiry time and the refresh token values, so the class can renew expired tokens.
Also read this article if you want to access the API when the user is not present.
phpclasses.org/blog/package/7700/po
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