The game "Volk-san: egg and catch", got the itchio url with "egg?ac", but if you click the link from the Bundle for Ukraine page, then you get sent to "egg" instead with a "page not found".

.. after a lot of looking around I found their youtube with the full link, as the game is currently off sale, and I also found it from my bundle page with a download link ^^ but still .. it should have sent me to the correct page from the bundle sale page.

Anything after the ? character in a URL are the page parameters. A page will never generate a URL with ? in it. The ?ac parameter you mentioned is the “affiliate code” parameter used with our partner system that will attribute any purchases to a specific account.

Oh .. wait a minute .. the egg page works .. hold on .. *goes in incognito mode and opens page again* .. Ah .. I wasn't logged in the first times I tried it, and the page is hidden for everyone that haven't bought it ..

It all makes sense now~