To get started, go to the Integrations page, find the Klaviyo integration, and click the "Connect" button next to it.
A popup will ask you to input an API key that you'll have to generate in Klaviyo by following this quick step-by-step guide (or access this link to reach the needed category instantly):
Click your account's name from the top-right corner of your screen and access the "Account" page.
On the Account page, go to the Settings section, and in the sub-section, access "API Keys".
Of course, you can use an existing API key, but we would strongly suggest generating a new one by clicking the "Create Private API Key" button.
Choose the "Custom Key" option and offer "Read" access to "Catalogs", "List", "Profiles" and "Segments".
Once the key is created, you can rename it to Retently, instance, so that it's clear where this particular key will be used.
Finally, copy the key, add it to the authentication popup in Retently, and hit the "Connect" button.