403 Forbidden

Hello everyone,

I need your help with this error:

Forbidden.

Request:
GET https://us21.api.mailchimp.com/3.0/?fields=account_id

Response:
403 Forbidden

Access Denied

You don't have permission to access "http://us21.api.mailchimp.com/3.0/?" on this server.

Reference #18.d891402.1744738861.6b490d37
https://errors.edgesuite.net/18.d891402.1744738861.6b490d37

The API key I’m using was created from an admin account and is brand new.

I already contacted Mailchimp (I saw in some posts that I might be blacklisted from their servers??), but no luck—they redirected me to the plugin's support, saying that since it’s a third-party tool, it’s not their responsibility.

Any ideas?