Hi Lap,
in the end I deactivated and deleted both plugins and started from scratch. This time I hide the MailChimp for Woocommerce checkout form and used your checkout integration.
All works fine now. Thanks very much for your help.
Hi Lap,
Thanks for such a quick response. The site is https://www.daverandall.art/.
You just need to pick a product and go to checkout. The Subscribe checkbox is from the MailChimp for Woocommerce plugin but there are actually 4 instances of a Mailchimp for WordPress v4.8.7 form in the source.
I have created a form using your plugin for use at the bottom of every page which is working fine.
The checkout subscribe is not working. I wondered if the plugins are interfering with each other.