Apollo
Setup
To setup your Apollo integration go to Settings->Org Settings->Integrations->Enrichment->Apollo.
To start, you will need your Apollo API key. This can be found my logging into your Apollo account -> Enrich -> Request API key. If you have trouble find the API key, you checkout Apollo's support page on the topic.
Enter your Apollo API key.
Click the toggle button if you wish to have Signals generate a contact list for you.
Ensure the integration is turned on at the top right of the page and click save at the bottom left of the page.