I\'ve been searching for days and trying new and older version of google-api-php-client along with various other examples out there, but I can\'t seem to get around this err
I'm pretty sure you need to write the phrase 'notasecret' somewhere in this section of code:
$key = file_get_contents($key_file_location);
$cred = new Google_Auth_AssertionCredentials(
$service_account_name,
array('https://www.googleapis.com/auth/books'),
$key
);
'Where?', is the question...
This looks like it has the correct code: https://github.com/google/google-api-php-client/blob/master/src/Google/Auth/AssertionCredentials.php
I will update my answer to confirm this works once I have tested it.
:)