Mailchimp

Mailchimp server prefix is the URL prefix before .admin.mailchimp.com

When connecting Mailchimp, pass the correct server prefix. It is the part of the Mailchimp URL before .admin.mailchimp.com. For example, if the Mailchimp URL is https://us19.admin.mailchimp.com/, the server prefix is us19. A wrong prefix can cause Mailchimp API calls to fail even if the API key/token itself looks correct.

Use subdomain or dc, not server_prefix, for Mailchimp connectionConfig

For Mailchimp API connection configuration, send connectionConfig.subdomain with the server prefix value, or use the legacy alias dc. Do not send server_prefix; that key is ignored by the validator and may fall back to a default such as us21. The UI label may say Server Prefix, but the API field name is subdomain.

Some Mailchimp tools require at least the Mailchimp Essentials plan

If Mailchimp tools fail despite the connection looking correct, check the customer's Mailchimp plan. Some Mailchimp API/tool capabilities require at least the Mailchimp Essentials plan. A free Mailchimp account may not be enough for the requested tool flow.

Mailchimp Proxy Execute with raw access token also needs subdomain

When using Proxy Execute with Mailchimp custom connection data, include both the OAuth access token and Mailchimp subdomain/server prefix. The endpoint can then be called through /api/v3/tools/execute/proxy with toolkitSlug: "mailchimp", authScheme: "OAUTH2", and val containing access_token plus subdomain such as us20.

Mailchimp has trigger support in the supported-trigger toolkit list

Mailchimp appears in the supported-trigger toolkit list. Before using a specific Mailchimp trigger, verify that the exact trigger or event exists in the current toolkit. If it does not, submit the use case through the Composio request portal.