Contact cannot be added without lists errror persists

Upon user registration, I have the “single checkbox” selected, along with a highlighted list and the default state of the checkbox as checked, yet every signup yields this error:

WP_Error Object
(
[errors] => Array
(
[nolists] => Array
(
[0] => A contact cannot be added without lists.
)

)

I would also note that when I return to the Registration Form options page I cannot see the option to select a list, unless I toggle between options (if I select “List of Checkboxes” then flip back to “Single Checkbox” I am again able to see the other associated options (Opt-in By Default, Select a List, etc).

Any help? I’m running the most recent version, php version is high enough, credentials valid. Thanks!

https://ww.wp.xz.cn/plugins/constant-contact-api/