API: create release link with ftp address return 400 bad request

I use GitLab CE on premise v11.7.4.

calling the API for create a release link with an ftp link url return 400 bad request.

api url:

http://<host>/api/v4/projects/<projectId>/releases/<tagName>/assets/links

post data:

name: "test"

url: "ftp://myftpAddress" <--- !!!

if set an http url it work fine.

There is a workaround?

Thanks