Overloop has a public API that allows you to create custom integrations to retrieve data from your Overloop account and add new data.
You can find Overloop API Reference here.
Where do I find my API key?
You can find the API keys in the Settings > API (for admins only).
For the users on the old pricing model, it is accessible on the Business plan only.
To connect Zapier, you can find the API key in Integrations Marketplace > Zapier.