Error with Facebook Pixel and WP Forms

Hi,

I get an error page when submitting a WP Form while the FB Pixel Plugin is active.
The messages still come through but the user gets the following error on a white page instead of being forwarded to the “thank you” page.

Warning: Illegal string offset 'first' in /wp-content/plugins/official-facebook-pixel/integration/FacebookWordpressWPForms.php on line 112

Warning: Illegal string offset 'last' in /wp-content/plugins/official-facebook-pixel/integration/FacebookWordpressWPForms.php on line 112

Warning: Cannot modify header information - headers already sent by (output started at /wp-content/plugins/official-facebook-pixel/integration/FacebookWordpressWPForms.php:112) in wp-includes/pluggable.php on line 1265

Warning: Cannot modify header information - headers already sent by (output started at wp-content/plugins/official-facebook-pixel/integration/FacebookWordpressWPForms.php:112) in /wp-includes/pluggable.php on line 1268

(I deleted the website details in the URL)

When I deactivate the FB Pixel Plugin it works fine.