I don’t have any caching plugins that Im aware but can’t say for sure as I have bought a theme which came bundled with some plugins.
I do have WooCommerce Services plugin
Hi I have the same issue, when pasting my API key and pressing save nothing happens. Checked on Mail Chimp and there is no API request
Wordpress version 4.9.8
Mail chimp plugin Version 2.1.9
Site Hosted on fasthosts.co.uk
Thanks
David Lyons