Fatal error on mailgun lists page

https://www.flowpress.com/screenshots/screenshot%202021-02-17%20at%206.52.58%20AM.png

https://www.flowpress.com/screenshots/screenshot%202021-02-17%20at%206.53.04%20AM.png

Your mailgun lists page under settings is throwing a fatal error , please get this fixed.

Call stack:

Mailgun::api_call()
Mailgun::get_lists()
include()
MailgunAdmin::lists_page()
WP_Hook::apply_filters()
WP_Hook::do_action()
do_action()
require_once()