Creating Segmented Welcome Series for Newsletter Popups

Hi all - quick help. Searched docs and youtube vids, no luck. I have a newsletter popup capture on my home page (exit intent) and on my blog (scroll depth). I need to create a different welcome series for both. I see I can setup a condition with the on subscribe but don't see how I can segment the api end point. also I see I can set the trigger to "add by api" and it gives me publicationID and automationID. Does this mean I should put this info directly in the api call on the pop up. I also see I can potentially add a tag to the pattern, "api|homepage" for example -- and then I can segment. What's the way this is usually handled?