If I try to refresh the 'access_token' I always get a php warning:
"Warning: array_key_exists() expects parameter 2 to be array, null given in <path>/createsend-php-4.0.2/class/transport.php on line 299"
Same for the lines 303 and 307
The warning happens just after:
"list($new_access_token, $new_expires_in, $new_refresh_token) =
Except to this waring everythings seems to work fine: I get a new access_token that I can use without any errors.
Would you be able to send more of the code to firstname.lastname@example.org? Unfortunately I'm not able to reproduce the warning you are seeing so I'd like to take a closer look at what you are sending through.