Add to an audience in Mailchimp when a link in an email is clicked in SendGrid

What each client fills in

Mailchimp: Audience ID

For example Audience → Settings → Audience name and defaults

The accounts it needs

Each is the client’s own, stored encrypted and never copied between clients. Until one is added the client’s checklist shows it, and nothing runs.

• 

  SendGrid → Settings → API Keys → Create API Key with Mail Send access; for the triggers, also the Event Webhook settings permission (user.webhooks.event.settings.read and user.webhooks.event.settings.update), or Full Access. The From address must be a verified sender.

• 

  In the client’s Mailchimp: Profile → Extras → API keys → Create A Key. The server prefix is the part after the dash (us21).

After you install it

It lands switched off. The client’s checklist holds exactly this:

1. Connect the client’s SendGrid, for “A link in an email is clicked”
2. Connect the client’s Mailchimp, for “Add to an audience”
3. Fill in Mailchimp: Audience ID (For example Audience → Settings → Audience name and defaults)
4. Confirm with the client: Click tracking is on in the client’s SendGrid: an untracked link sends no click.