Mailchimp API Connection Failing

[iversoncreative]

Describe the bug
This seems like a bug, but please forgive me if it's not. We've had to update the Mailchimp API key due to personnel changes.

When attempting to connect the MailChimp API in the Connections settings, it always returns a 'Mailchimp: The response is not a valid JSON response' error for the new API key.

Also getting a 'Failed to load resource: the server responded with a status of 500 (Internal Server Error)' for https://searchlightnm.org/wp-json/newspack/v1/oauth/mailchimp?_locale=user.

We are hosted with Wordpress.com, WordPress version 6.5.2, Newspack version 3.6.10, PHP version 8.1.28.

To Reproduce
Steps to reproduce the behavior:

1. Go to Connections
2. Click on Connect in the Mailchimp APIs section
3. Enter API key
4. Click Connect button
5. See 'Mailchimp: The response is not a valid JSON response' error

Screenshots

Expected behavior
It is expected that the API connects successfully. All other Connections are working as expected.