EDIT: this was a try to upload Monsterhythm (Pico-8 cartridge). I can't find the option to erase the post, so I moving it to support. Sorry for the inconveniences! :(

you need to put the cartridge tag in the text, not the tags field =)
bit confusing!

Sorry, this cartridge is not currently available.

by

Cart #12916 | 2015-08-23 | Code ▽ | Embed ▽ | No License

Thanks impbox! Zep told me the same on twitter. Now I'm editing the post but it still doesn't appear. Probably I'm missing something else?