concurrent request in asp.net server (iis )

I am facing a problem with IIS 10 (on windows server 2019) . I have a web API developed using asp.net and published to windows server 2019 (server A) . It is being consumed from another Server in the same LAN network (server B) . The problem is when the number of requests per second(concurrent requests) reaches 50 , for example, server A can process 14 requests/second. Server A has a huge resource that makes it capable of processing more than 100 requests/second. I do not know what is the reason and how the solution should be .