Facebook purchases in HubSpot
We have a website that sells courses on teachable. Let's say that webiste name is abc.com (we have HubSpot tracking code installed on it). When you get to the website and click "Buy No" you get redirected to teachable site https://sso.teachable.com/abc.com
After they purchase the course they get redirected to our thank you page. Example: abc.com/thank-you. We'd like to which channel attributed last to the purchase. We run Facebook ads, AdWords, Reddit ads, Twitter, do a lot of SEO and we have hard time figuring our which channel actually was "last click attribution" channel.
Any ideas how we could tackle this problem? Are we maybe missing some "special" code on the thank you page that will tell hubspot where the sale came from?