Not possible to post *.jotform.US links in Twitter

One user reported in Twitter:

" @JotForm Twitter no longer accepts your form links in tweets. You may want to look into this. "

I have tried to reproduce this, and found that Twitter is not letting you to post links related to *.jotform.us domain.

For example, you can not post:

http://form.jotform.us/

http://www.jotform.us/

Twitter warning:

" This request looks like it might be automated. To protect our users from spam and other malicious activity, we can't complete this action right now. Please try again later. "

Thank you.

I have contacted twitter about it. It might a phishing form or a spammer or maybe because too many people posted with URLs with jotform.us in it. I have reviewed recent tweets but couldn't find an offending tweet.