Maybe this will help:
I've heard of using barkeeper's friend as well but I've never used it on copper.
This may help: https://www.hometalk.com/28611511/how-to-clean-copper-bottomed-pots
Essentially an abrasive coupled with an acid, are what is typically used.
Hello Valjean, hope this helps you
You are most welcome!
I've used ketchup, and also tried salt on half a lemon. Both require some elbow grease, a bit of scrubbing and a good rinse. Dry it when you are done.