For running J!5.1 you must https://fabrikar.com/forums/index.php?wiki/update-from-github/ or include the new file manually https://fabrikar.com/forums/index.php?threads/joomla-5-1-and-fabrik-cannot-find-files-error.54473/post-285151 See also Announcements
Please see our announcement here.
require_once JPATH_ROOT . '/libraries/fabrik/fabrik/fabrik/Helpers/sms_gateways/twilio.php';
use Twilio\Rest\Client;
Gentle reminder to include Twilio Library in next update.We can include the Twilio library in the next update but I imagine most people who need it would also want the SMS plugin.