Unfortunately this will be hard to debug remotely, since you need to redact the access token itself, for the sake of security.
Where did you get the access token and how are you loading it though? Can you double check there aren't any stray characters on it? E.g., if you copied and pasted it from somewhere, make sure there aren't any invisible characters that got included. You could try copying it in to a plain text editor to make sure you only have plain text.
For reference, access tokens should look like this: