nginx limit_conn_zone doesn't work in my server - apache

Question

I try to apply limit_conn to my server for test purposes but it doesn't work.
There is my nginx.conf
events {}
http {
include mime.types;
limit_conn_zone $binary_remote_addr zone=addr:10m;
server {
listen 80;
location /downloads/ {
limit_conn addr 1;
return 200 "Hello";
}
}
}
Then I run Apache Benchmark
ab -n 10 -c 10 http://MY_IP_ADDRESS_OF_SERVER/downloads/
I get this output data:
This is ApacheBench, Version 2.3 <$Revision: 1757674 $>
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Licensed to The Apache Software Foundation, http://www.apache.org/
Benchmarking MY_IP_ADDRESS_OF_SERVER (be patient).....done
Server Software: nginx/1.16.1
Server Hostname: MY_IP_ADDRESS_OF_SERVER
Server Port: 80
Document Path: /downloads/
Document Length: 16 bytes
Concurrency Level: 10
Time taken for tests: 0.004 seconds
Complete requests: 10
Failed requests: 0
Total transferred: 1760 bytes
HTML transferred: 160 bytes
Requests per second: 2693.97 [#/sec] (mean)
Time per request: 3.712 [ms] (mean)
Time per request: 0.371 [ms] (mean, across all concurrent requests)
Transfer rate: 463.03 [Kbytes/sec] received
Connection Times (ms)
min mean[+/-sd] median max
Connect: 1 2 0.3 2 2
Processing: 0 1 0.6 1 2
Waiting: 0 1 0.5 1 2
Total: 2 3 0.3 3 3
Percentage of the requests served within a certain time (ms)
50% 3
66% 3
75% 3
80% 3
90% 3
95% 3
98% 3
99% 3
100% 3 (longest request)
But I expect to get in output something like this
Complete requests: 10
Failed requests: 1
Non-2xx responses: 9
It seems that limit_conn doesn't work in my server. Why doesn't it work and how can i solve this problem?