HackerOne users: Testing against this community violates our program's Terms of Service and will result in your bounty being denied.
Subscribing to newsletter on vanillaforums.org
smokvinlist
New
in Feedback
I guess, some debug information left 
This is what I got displayed on top of page:
MCAPI::listSubscribe('91854571ea', 'xxx@xxx.com', 'Array(1)', 'html', '', '1')
0