Hi, ailen 

Thanks for reaching out to us.

This could be an issue with the SSL certificate on your site.

There is a workaround for this issue.

You can edit a PHP file on your FTP in the plugin folder, with any text/code editor.

This is the path of the file :

 ../wp-content/plugins/wpdatatables/controllers/wdt_admin_ajax_actions.php

 around line 1089 ( during updates the exact lines of code change, so i recommend searching  for string "curl_setopt" with CTRL+F"), you will find this line of code:

curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);

then add this below that :

curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 0);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 0);

in the end it should look like this :

And it will bypass the SSL issue, and activate the license. 

Please note, though, that if you migrate the site in the future, and the SSL certificate is not updated, you'll need to add this line again.

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Let me know how it goes?

If that does not help, we can remotely take a look. Thank you