Unsubscribe API Push/Pull

I’m needing help finding where the API documentation is so that I can send emails that have unsubscribed from my website to the Infusionsoft system to suppress them. I’m also wanting to pull users who have unsubscribed through Infusionsoft to my system. (Something like a once a day API call back and forth.)

Start with which api you’re using? Legacy, XML-RPC, REST?

There’s an opout option in each, you could tag them or pull a list with the api.