Error message

• The MailChimp PHP library is missing the required GuzzleHttp library. Please check the installation notes in README.txt.
• Notice: Trying to get property of non-object in mailchimp_lists_field_formatter_view() (line 515 of /home/robreit107/domains/airsoftunited.be/public_html/sites/all/modules/mailchimp/modules/mailchimp_lists/includes/mailchimp_lists.field.inc).