This could be because your domains last owner [If there was one] used it for not allowed stuff, or a similar reason.
Facebook does not allowed sites listed as scams or dangerous here:
https://www.mywot.com/
And also check here if your domain was used in the last years.
https://archive.org/
If it was used, you will be able to see what it was used for.
These are just checking tools, but they will help you in the future, to check a domain before buying it.