Unable to add new subscribers

[JLNNN]

Whenever I enter some data into a form, there's no visible response that I forgot some fields or something like that. No error log entries, no hidden code. I removed the default required fields and just entered "email".

TYPO3 7.6.14
direct_mail_subscription: current dev version (2.0.3 has the same problem)
tt_address: 3.2.1 (3.0.3 didn't work, too)

Any advice would be appreciated, thank you :)

[JLNNN]

Can be closed, I guess it's a https // http mistake on our side. THX :)