This component in the plugin for postbit_display_start throws an error in PHP 7.3:
Code:
eval('$template_hook[postbit_end] .= " ' . fetch_template('post_thanks_box') . '";');
Error:
Code:
PHP Warning: Use of undefined constant postbit_end - assumed 'postbit_end' (this will throw an Error in a future version of PHP) in ..../includes/class_postbit.php(268) : eval()'d code(23) : eval()'d code on line 1
All you need do is add some quotes around postbit_end:
Code:
eval('$template_hook["postbit_end"] .= " ' . fetch_template('post_thanks_box') . '";');