Increase Sping boot RPS to 200 RPS

Question

I am making API request to a 3rd party API where we have to make around 1 million requests , I have tried to scale max connection to 2000 but still my rps reach up to 300 rps only, I have also annotated my method to @Async

Also I have added server.tomcat.threads.max=500 in properties file but yet it doesn't cross 300 rpc mark.

CloseableHttpClient httpClient = HttpClients.custom()
                .setMaxConnTotal(2000)
                .setMaxConnPerRoute(200)
                .build();