There are 2 ways to purchase GC (Gold Coins), first there is the website, where you purchase over Xsolla and the second one is Steam.
Sometimes there can be an issue purchasing anything on both ways.

Steam

• If you get a "PLEASE WAIT" message for longer than normal when trying to buy it, try the following:
  1. Check on your Steam settings if it's enabled. 
  2. Check if it's also enabled for the game (right click Infestation: The New Z in your library and go to Properties)
  3. Make sure you're running Steam.exe and GameOverlayUI.exe as admin.
  4. Make sure you're running TheNewZ.exe and NewZLauncher.exe as admin.
  5. If those don't work, try setting TheNewZ.exe to run in compatibility mode to a different Windows version (Windows Vista usually works).

Website

If you are having issues with a GC purchase, please contact xsolla.com so they can assist you live with the issue.

If you need any help or these points didn't work, please submit a ticket at playnewz.com/support