This version 1.1 update should not be used, it has a number of issues:
The function get_value_for_api() is where the problems are:
$taxonomy variable used on 351 is never defined. You need to set $taxonomy = $field['taxonomy']; before the loop online 348.
In addition, the $taxonomy variable is not passed to get_terms, making the function fail and return nothing (line 350).
If you do fix these bugs and get the plugin working again, it now returns data in a different format. It used to return an array of category ids (useful), now it returns a string of category names (useless, if you need to get the term objects).
This change to the API is documented in the changelog, but as far as I am concerned it is an unacceptable change.
I appreciate the work the author has put into version 1.0 of this plugin, I love it. However 1.1 is not an upgrade you should make.