This all references more current versions of Mautic but its a start.
There is no need to install any additional plugin to your Mautic instance. Zapier works with the API and webhooks already available within Mautic. This Zapier integration use Basic Authentication to access Mautic API. It is disabled by default so enable this first.
Open the admin menu
Go to Mautic’s global configuration
Go to API Settings
Set API enabled? to Yes .
Set Enable HTTP basic auth? to Yes .
Save the configuration.
Run a test on your domain here to troubleshoot SSL errors as well.