For connecting ReStock Alerts to Klaviyo, you need your Klaviyo account's private and public API keys.
To find this you need to log in to your Klaviyo account.
On the top right corner, you should click on your shop name.
Select "Account".
Under Setting, you'll see the API keys option.
By selecting it, you can see the public and private API keys.
If there's no private key, select Create Private API Key, to create one.
And that's it!