/api/add/
Creates a new shortlink for the given url. If the same
URL already exists for the same user_id and domain, the
existing shortlink is returned instead (idempotent). The properties user_id, domain, use_mp4, and alias are
OPTIONAL. If alias is provided, it must be 3-50 alphanumeric characters (letters and numbers only); if it's already taken, the request returns a 400 Bad Request error. Omitting domain picks a
random configured domain.