311 Your list has an email type option, so the text part is required

I’m getting this issue too. Evidently it’s because WordChimp isn’t generating the plain text version of our campaigns.

https://groups.google.com/group/mailchimp-api-discuss/browse_thread/thread/20a1e73bd78081c8?pli=1

I don’t have any idea how to fix it, unfortunately, but maybe the developer will see this and fix it.

Here is how you fix it. In mailchimp there are settings for each list. In those list settings, you will find a section called List Name and Defaults. In that section, there is an option to let users choose an email format: Let your subscribers pick an email format?

If you uncheck this option, mailchimp will process the post without complaining.