There was an update of the mailgun api, i don't know if the plugin is still compatible.
I think the api url just has to be change to /v3
Mailgun Blog

Looks great! Personally i will stay at the old design because it's not that casual forum design. But it looks very clean and i love the mobile version . I will defiantly use it in a project.

Hi, few weeks ago i migrated my Joomla Website with a Kunena Forum to NodeBB.

It's a german developer and gaming community.
http://mytechzone.eu

I'm new in the NodeBB-Universe and atm im porting my website from Joomla+Kunena to NodeBB. I would really love to see this plugin in the 0.6 Version of NodeBB so my community can use the cash-system for useful stuff. On my last website I had a "points"-system and I always wondered what to do with those points. I never had an answer to that, ... ^^

Anyway, this plugin looks awsome!