To connect Big Business to HubSpot you need to log into your Hubspot Dashboard to create an API Key.
This Solution tells you how to generate an API Key. (7402)
To create credentials for HubSpot:
1. Go to your Hubspot Dashboard
2. Go to Settings, Integrations, API Key
3. Click the button to "Create key".
HubSpot will generate an API Key.
4. Click Copy to copy and then Paste into Big Business.
Copy the Key into HubSpot Settings in Big Business.