It says it happens at the end of any turn your opponent took damage, but it certainly isn’t working at the end of your turn. I think it might be working at the end of your opponent’s turn if you manage to deal damage to them on their turn, not positive though.
Hello @stikxs ,
Thank you for all the information provided, this issue will be investigated!
If you have any additional information that you consider relevant, please don’t hesitate to send me 
Rebeca.