use Int64.of_string_opt

src/http_info.ml

@@ -234,12 +234,12 @@ let keys req server _env =
     let* last_issue_date =
       match Vif.Queries.get req "last_issue_date" with
       | [] -> Ok None
-      | v :: _ -> (
-          match int_of_string_opt v with
+      | s :: _ -> (
+          match Int64.of_string_opt s with
           | None ->
               Error
                 "invalid `?last_issue_date` query param, int_of_string failure"
-          | Some n -> Ok (Some (Time.Timestamp.of_s (Int64.of_int n))))
+          | Some n -> Ok (Some (Timestamp.of_s n)))
     in
     let* v = mk_keys ~db_conn keys ~last_issue_date in
     let s = Api.encode_exn jsont v in