API URL and KEY error

Hello!
I am trying to connect my WP site to ActiveCampaign account with API URL and KEY.
And when I click on ‘connect’ after filling the details, this message is shown-
{“msg”:”Invalid request, security validation failed.”,”status”:false}

I contact with ActiveCampaign support and they cannot fix the problem, they said it’s something wrong with my WP.
Thanks for the help 🙂