MC4WP + CF7 integration: getting 404 error from MailChimp

Hello,

I have a CF7 contact form containing the [mc4wp_checkbox subscribe] shortcode and prefixing various other fields with mc4wp_.

All worked as expected in staging, but on migration to production I’m seeing a 404 error in the mc4wp logs when the form is submitted with the checkbox checked.

Any idea what might be going on?

Thanks,
Jon

Example from logs:

Request:
POST https://us20.api.mailchimp.com/3.0/lists/74d4662eeb/members
{“status”:”pending”,”email_address”:”t8@te***.com”,”interests”:{},”merge_fields”:{},”email_type”:”html”,”ip_signup”:”82.23.132.236″,”tags”:[]}
Response:
404 Not Found
{“type”:”https://mailchimp.com/developer/marketing/docs/errors/”,”title”:”Resource Not Found”,”status”:404,”detail”:”The requested resource could not be found.”,”instance”:”0f25ffb5-f331-4598-aa2e-0a5c03761fbc”}

The page I need help with: [log in to see the link]