Reconnect your Mailchimp Account
Mailchimp is moving from OAuth to OAuth 2.0, a stronger authentication method that does not require users to provide API keys. It has the ability to share data without the need to release personal information.
The current Oauth method will be disabled on June 16th, 2021 so it’s important that you reconnect your Mailchimp account as soon as possible to avoid any disruption.
Login to your Mailchimp account → Select Allow.