depends. Is this for a particular integration or a generic API to a custom db?
It is to MS Marketplace. We are capturing the leads, but it isn't capturing to the program for some reason.
1. What isn't my smart campaign capturing the new leads?
You would have to show us the SC trigger (Smart List) screenshot and the details of an activity in a lead's ActLog.
2. How do I set up the smart campaign to capture both net new leads and the form fills through the API that are not net new (these will not have the new lead source).
Why would they not have the new lead source? Isn't the lead source being set by the API consumer? Have you blocked field updates from the API user?