Getting "io.netty.channel.ConnectTimeoutException" In Gatling when ramping up load with high user count

Question

I want to test my APIs with high load. I have written load config like below:

setUp(
    scn.inject(
      nothingFor(2 seconds),
      constantUsersPerSec(250) during (300 seconds),
      rampUsersPerSec(50) to (100) during (60 seconds),
    ).protocols(httpConfig)

When I want to run 250 user and want to ramp it upto 300 seconds only, its giving me loads of errors. Can someone suggest to bypass the errors? I want to generate 1000calls/sec onto API but with this setup its barely going upto 200 calls/per in monitoring tool. I want to put 500K calls in 5-10 min duration but looks like basic one with 50K-70K is not working and giving errors/exceptions

I tried with constantUsersPerSec along with rampUsersPerSec