The Aiva Chat app for Zapier was only ever shared by invite, and we've now retired it. The Zapier card on the Integrations page, the Connect Zapier steps on the API keys tab and Zapier subscriptions on the Webhooks tab are gone.
What to use instead
Webhooks send the same events, signed and with a delivery log and retries, to any HTTPS URL. If you use an automation tool that gives you a webhook URL, point an Aiva Chat webhook at it. See Send Aiva Chat events with webhooks.