Strange error on add

I just installed the plugin and when I click add I get this error:

Fatal error: Uncaught GuzzleHttp\Exception\ServerException: Server error response [url] https://api.constantcontact.com/v2/lists?api_key=kawd2utg75a4aa7dgvvqzgjh [status code] 500 [reason phrase] Internal Server Error in /home/t3chs1co/public_html/wp-content/plugins/constant-contact-forms/vendor/constantcontact/guzzlehttp/guzzle/src/Exception/RequestException.php:89 Stack trace: #0 /home/t3chs1co/public_html/wp-content/plugins/constant-contact-forms/vendor/constantcontact/guzzlehttp/guzzle/src/Subscriber/HttpError.php(32): GuzzleHttp\Exception\RequestException::create(Object(GuzzleHttp\Message\Request), Object(GuzzleHttp\Message\Response)) #1 /home/t3chs1co/public_html/wp-content/plugins/constant-contact-forms/vendor/constantcontact/guzzlehttp/guzzle/src/Event/Emitter.php(108): GuzzleHttp\Subscriber\HttpError->onComplete(Object(GuzzleHttp\Event\CompleteEvent), ‘complete’) #2 /home/t3chs1co/public_html/wp-content/plugins/constant-contact-forms/vendor/constantcontact/guzzlehttp/guzzle/src/RequestFsm.php(91): GuzzleHttp\Even in /home/t3chs1co/public_html/wp-content/plugins/constant-contact-forms/vendor/constantcontact/guzzlehttp/guzzle/src/Exception/RequestException.php on line 89