Combining discount link + product page

[benchmarq1]

Hi guys, 

is it possible to combine discount link with certain product page? 

That´s my discount link: https://hoehlenhund.de/discount/BLACKDEAL25 
That´s the product page I´d like to target: https://hoehlenhund.de/products/hundehohle-universell

I´ve tried a few combinations but can´t see the discount in the check out area... any idea how to set up correctly? 

Thanks for helping out! 

best from Hamburg, Germany
Benjamin