We had the same problem with another customer, so just moved the site to a different server and it worked again.
Could our server’s IP-address be blocked somewhere? Customer support chat with Mailchimp:
It looks like a temporary block on that IP address could be caused by a high amount of requests or by our upstream provider Akamai if there was any detected suspicious activity on the IP address.
We unfortunately can’t say anything definitive without a Reference Number to check.
The integration that is being used might be able to help see the error response to the API call that would have a Ref #.
ME: which Reference Number?
We would need a reference number from our upstream provider Akamai to look up and provide some further information. That’s where Kriesi might possibly be able to provide the API call and reference that error message.
Is this something Kriesi can help with?!