Checkbox problems

When I use a single checkbox [checkbox name “option”] I get
Notice: Array to string conversion in /srv/www/wordpress-plani/wp-content/plugins/bootstrap-for-contact-form-7/classes/CF7BS_Form_Field.php on line 540

If there are more than one option [checkbox name “option 1” “option 2”] the problem goes away

https://ww.wp.xz.cn/plugins/bootstrap-for-contact-form-7/