Warning: preg_match() expects parameter 2 to be string, array given in Cleantalk

Problem/Motivation

Drupal 8.9.16
PHP 7.3.28

All update.php OK, cleared caches

Error after entering key and trying to "Save Configuration":
Warning: preg_match() expects parameter 2 to be string, array given in Cleantalk\Common\Helper::http__request__rc_to_host() (line 1323 of modules/cleantalk/src/lib/Cleantalk/Common/Helper.php).

Cleantalk\Common\Helper::http__request__rc_to_host('sfw_update', Array, Array) (Line: 249)
Cleantalk\Common\Firewall\FirewallUpdater->update() (Line: 675)
Drupal\cleantalk\CleantalkFuncs::apbct_sfw_update('gazy8a9utuju') (Line: 81)
Drupal\cleantalk\Form\CleantalkSettingsForm->validateForm(Array, Object)
call_user_func_array(Array, Array) (Line: 82)
Drupal\Core\Form\FormValidator->executeValidateHandlers(Array, Object) (Line: 273)
Drupal\Core\Form\FormValidator->doValidateForm(Array, Object, 'cleantalk_settings_form') (Line: 118)
Drupal\Core\Form\FormValidator->validateForm('cleantalk_settings_form', Array, Object) (Line: 589)
Drupal\Core\Form\FormBuilder->processForm('cleantalk_settings_form', Array, Object) (Line: 321).... etc.

Any ideas? It works on my local WAMP setup, but not on the production server

Thx

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes