Facebook report Site URL has been identified as malicious and/or abusive,
If you have abuse any of the guidelines of facebook https://www.facebook.com/ad_guidelines.php
Here is a form for appealing blocked content (in your case URL). However there are very few chances of getting unblocked your URL but still you may try this form and hoping to get reply from Facebook. In any case if your URL is unblocked there is a high probability that your future users will see a captcha when visiting your app from mobile devices. So I can recommend to change the URL and continue developing with other URL.