@mygreenfootprint If you’re needing to alter the submission in your plugin, that custom function can be inserted in your theme’s functions.php
file. Are you comfortable adding PHP code and altering to your needs? If not please consult with a developer to help you accomplish your requirements.
The root of the error is unfortunately very difficult for us diagnose remotely. Since we don’t have access to the servers that are running our plugin, our best attempt to show what went wrong was in the logger as you’ve pointed out above.
The error message you’re seeing can be triggered a few different ways, but one of the most common ones is when an email address has been banned ( which you said was not the issue ) and also when for example a “first name” and “last name” are “REQUIRED” on the list, but you’re not passing it through the submission. It could be any number of problems at the Audience merge fields level that the plugin would not be able to detect without some developer interaction.
I would also suggest reaching out directly to Mailchimp’s customer support team and tell them to turn on debugging for your account while you do a few tests to see if they can spot the problem a little quicker for you.
If you get responses from them and still feel that the plugin is the cause of this conflict, feel free to reach out to us again and we’ll open this back up for you.