Error Activating CleanTalk

CleanTalk was working well but after some caching problems caused me to deactivate the plugin temporarily, I got the following error when trying to re-activate. I uninstalled and then re-installed the plugin but am still getting the error.

Fatal error: Uncaught Error: Undefined constant “Cleantalk\ApbctWP\CURLOPT_USERAGENT” in /home/weencehost/public_html/wp-content/plugins/cleantalk-spam-protect/lib/Cleantalk/ApbctWP/Helper.php:42 Stack trace: #0 /home/weencehost/public_html/wp-content/plugins/cleantalk-spam-protect/lib/Cleantalk/ApbctWP/Helper.php(62): Cleantalk\ApbctWP\Helper::httpRequest(‘https://weence….’, Array, ‘get_code’) #1 /home/weencehost/public_html/wp-content/plugins/cleantalk-spam-protect/inc/cleantalk-pluggable.php(947): Cleantalk\ApbctWP\Helper::httpRequestGetResponseCode(‘https://weence….’) #2 /home/weencehost/public_html/wp-content/plugins/cleantalk-spam-protect/lib/Cleantalk/ApbctWP/Activator.php(15): apbct_settings__get_ajax_type() #3 /home/weencehost/public_html/wp-content/plugins/cleantalk-spam-protect/cleantalk.php(424): Cleantalk\ApbctWP\Activator::activation(”) #4 /home/weencehost/public_html/wp-includes/class-wp-hook.php(307): apbct_activation(”) #5 /home/weencehost/public_html/wp-includes/class-wp-hook.php(331): WP_Hook->apply_filters(”, Array) #6 /home/weencehost/public_html/wp-includes/plugin.php(474): WP_Hook->do_action(Array) #7 /home/weencehost/public_html/wp-admin/plugins.php(194): do_action(‘activate_cleant…’) #8 {main} thrown in /home/weencehost/public_html/wp-content/plugins/cleantalk-spam-protect/lib/Cleantalk/ApbctWP/Helper.php on line 42

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