Internal Campaign Tracking possible?

As I’ve read, a campaign is only tracked from an external URL, so I don’t know how to track an internal campaign.
My customer has some campaigns on his main page (product offers). Within this campaign there can be multiple products, that the visitor can add to his basket. Finaly my customer wants to know, which campaign on the starting page works best, means how many conversions und which value was generated. Any idea?

For this I would use Custom Variable on a scope “page” to track for example name=“starting” value="/products/test1", name=“previous”, value="$previous_page"

Note: you could even use Javascript to set the previous page URL as a custom variable value in piwik js code.

See: Custom Variables Analytics - Analytics Platform - Matomo

Then you will get for all conversions, number of values “Starting” and “Previous” and top values / Page names for Ecommerce conversions.