Fatal Error

I have your plug-in running with the same configuration on 3 sites using GravityForms and Mailpoet, for some reason one site is now showing the following error – any ideas on cause? Seems to suggest no list data being sent, but it is?

Fatal error: Uncaught Error: Argument 2 passed to MailPoet\API\MP\v1\API::subscribeToLists() must be of the type array, null given, called in /var/www/vhosts/farmcontractormagazine.com/httpdocs/wp-content/plugins/add-on-gravity-forms-mailpoet/class-gfnewmailpoetaddon.php on line 215
in /var/www/vhosts/farmcontractormagazine.com/httpdocs/wp-content/plugins/mailpoet/lib/API/MP/v1/API.php on line 126

Thanks

Matt

The page I need help with: [log in to see the link]