If you are trying to share a website link (yours or others) and if Facebook is blocking you from sharing it, then it’s kinda blacklisted by Facebook for some reasons. Their security systems will detect it as an unsafe link.
Maybe it’s reported by several Facebook users or it’s spammy overall, if your website is innocent and if you want to be unblocked, then you can try this official form.
If the above form link is not working, kindly try this form then.
P.S. I used my personal blog URL (https://pradeepkumars.com) just for watermarking purpose, it’s not blocked by Facebook, yet.