Hello,
Please try to set options Use AJAX for JavaScript check to Off and Use static keys for JavaScript check to Auto here:
WordPress Dashboard -> Settings -> Antispam by Cleantalk -> Advanced settings
Did it help?
I changed the settings but the error is still showing up
Please, deactivate the plugin with the “Complete deactivation” option enabled and then activate it again.
1. Enter the Antispam by Cleantalk plugin settings. (WordPress Dashboard -> Settings -> Antispam by Cleantalk -> Advanced settings)
2. Check the last settings “Complete deactivation” and save changes.
3. Deactivate the plugin on the “Plugins” page in WordPress Dashboard.
4. Then activate it.
5. Proceed to the plugin’s settings. (See item 1.)
Did it help?
I checked again after clearing cache and your first suggestion has worked. Thank you and Merry Christmas!