Are you asking which ‘keyword - Google term’ a user used to make a purchase? If that is the case, you will need to implement Google Analytics 4, Server-Side Facebook CAPI, Google Search Console, and other similar tools, which are outside the scope of Django but are necessary to effectively track your sales and your marketing activities.
So, the free tool is Google Analytics. It shows user’s source/medium, dig to some reports and if you have setup proper conversion tracking, you will have your data.