Iterable

In Iterable, obtain a Standard (server-side) Iterable API key by going to Integrations → API Keys → New API Key. For more detail please review Iterable's instructions.
In Polytomic, go to Connections → Add Connection → Iterable.
Paste your Iterable API key in Polytomic's API key field.

Click Save.

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Iterable Permission Requirement
Iterable only allows API Keys to be managed by Org Admins or members with the Project Configuration > Data Feeds, Third-Party Integrations, API Keys and Webhooks permission