Hello @darcheville95,
In order to authenticate to the Stuart API you still need an access token.
As explained in our documentation this token has an expiration time of one month
until when it needs to be renewed.
If you try to authenticate with a token that has expired, you will indeed receive an error of type “INVALID_GRANT”.
To handle such errors in the future, make sure you have a retry mechanism in place that allows your token to be renewed.
You can read this post to learn about our best practices for authentication.
Thank you for your message