How to Integrate OptinMonster with Mailchimp

This connector is on every OptinMonster plan. Official page: How to Connect OptinMonster with Mailchimp. Attach MonsterLeads as a backup.

Connect your audience

1. Create an API key in Mailchimp (Mailchimp's own key guide).

2. In the campaign builder, open Integrations, search for Mailchimp.

3. Enter an internal account name and the API key. Click Connect to Mailchimp.

4. Under Email Provider Lists, pick the Audience. Required.

5. Optional: leave Enable Double Opt-in? on (the default) or turn it off for single opt-in. Optional: pick tags that already exist on that Audience.

6. Save.

Turning off double opt-in does not flush the pending queue. Addresses captured while it was on still wait for the confirm click.

Mailchimp groups

Groups have to exist in Mailchimp first.

Automatic: Integrations → Mailchimp → add a Group Label (not shown to visitors) → set Groups Selection Type to Hidden → tick the groups every new lead should join.

Visitor-picked: same panel, set the type to Visible. The label shows on the form. Use checkboxes for multiple groups or radio buttons for one. You can reorder, pre-tick or hide options.

Test with a unique address every time. Mailchimp will not re-subscribe an unsubscribed or deleted address through the API. For that path, embed a Mailchimp-hosted form with the Form Embed block.

A "merge fields were invalid" error usually means Mailchimp requires FNAME (or similar) and the campaign does not send it. Check the form field and merge-tag mapping first. Before changing an audience-wide required flag, consider other forms and workflows that depend on that requirement. Phone numbers only land if the merge tag is literally PHONE.

Verify the complete signup flow

These are editorial acceptance checks, not results from a tested account. Use controlled test addresses and record the campaign, audience and outcome. For a form with multiple group choices, test each route instead of checking only the default choice.

Treat connection, confirmation and follow-up as separate stages. A missing welcome email calls for a different investigation from a contact placed in the wrong audience. Avoid changing multiple settings at once: reproduce the failure, change the relevant setting and repeat that specific test.

Prepare a useful handoff

Document which audience owns the campaign, which tags or groups it applies and who maintains the follow-up. Keep API keys out of the handoff. Recheck the receiving record after changing the audience or form fields; a previous successful test applies to the configuration that was tested.

Source checked September 6, 2026: OptinMonster Mailchimp documentation, which displays a March 13, 2023 update date. Compare documented controls with your account.

More connectors: OptinMonster integrations.