If you haven't already, you'll need to sign up for a Mailchimp account.
Setting up your Mailchimp API key
Navigate to the API keys screen, by clicking on your username in the bottom left corner and selecting 'Account'. Next, click 'Extras' and select 'API Keys'. (or click this shortcut)
Select all and copy the API Key field.
Paste in the API Key on your settings page under "Integrations"
You're all set!
💡 Tip: You can now head to the opt-in form support article to add/complete your opt-in form.
We support having up to five merge fields on an Opt-in form link. Think of a merge field as just another input on your link to collect information, like a first and last name.
Note: Make sure to test your Opt-in form link. If you receive an error about merge tags, make sure that the required fields in Mailchimp and Campsite match each other. If the "First Name" field is required on your Mailchimp signup form, it has to be required on your opt-in form link.
Adding a Tag
When adding a new contact to your audience, you can specify any tags you would like to be applied. This is useful for organizing your contacts internally. Check out Mailchimp's Getting Started with Tags for more info on tags.