I send only one request for the register command, and i send for the search request only 50 domains by 50 domains (we can 100 domain searches at the same time, no?)
If your script sends multiple requests to the api at the same time, you will get that error. You should send one request, wait for it to finish, and then send the next request.
We added this rule because some api users were sending thousands of requests at the same time, and slowing down the server.