In your HubSpot account, click the settings iconsettings in the main navigation bar.
In the left sidebar menu, navigate to Integrations> Email service provider.
Here, you'll find the most recent error as reported by Mailchimp, and a button to dismiss the error once it has been resolved. Some common errors include:
FNAME must be provided - Please enter a value
LNAME must be provided - Please enter a value
MMERGE2 must be provided - Please enter a value
MMERGE(x) must be provided - Please enter a value
These errors occur because the Mailchimp list has required merge tags for which HubSpot doesn't send a value. HubSpot will always push email addresses to Mailchimp since the email address for a contact is always known. If your forms include a first and last name field, HubSpot should capture this information and send it to Mailchimp as well.
To resolve these errors:
Log in to Mailchimp and locate the list your pop-up form or non-HubSpot form is connected to.
In the left sidebar menu, navigate to Settings > List fields and *|MERGE|* tags. The value in the Put this tag in your content column will correspond with the error reported in HubSpot.
Clear the corresponding Required?checkbox to allow HubSpot to push information to this list.