We've brought this up with the bundle organizer and they've recognized the issue. It should be fixed in the next few days! We'll let you know when that happens. Thanks!
Viewing post in Tiny Tales Pixel : Dungeons 2D Tileset Asset Pack comments
After some discussion with the organizer, it seems that they are unable to issue the key for some reason. As such, we'll have to ask you to send an email to megatilescs@gmail.com with a quick proof of purchase (A screen cap of the email received from Humble Bundle or your Humble Bundle page showing the purchased content) and we'll send the key your way. Thank you and sorry for the inconvenience!