You are getting message from Facebook, that they can’t validate the WebHook.

1 - Make sure you are on HTTPS ( ssl )

2 - If you use NGNIX, in some configs, the rewrite has an error

CleanShot 2023-12-06 at 00.17.05

Replace that code with

location / {
        try_files $uri $uri/ /index.php?$query_string;
    }