Cannot bind to port 80 with normal user despite setting cap_net_bind_service=ep on binary

I want to bind to port 80 using cap_net_bind_service using normal user. I enabled cap_net_bind_service capability on the binary using sudo setcap cap_net_bind_service+ep server Inside the code, I make sure the correct cap is set by writing out what the current caps are

cap_t cap = cap_get_pid(pid);
    if (cap == NULL) {
      perror("cap_get_pid");
    }
    caps_text = cap_to_text(cap, NULL);
    if (caps_text) {
        printf("capturing: %s\n", caps_text);
    }

And I got the expected output capturing: cap_net_bind_service=ep. When checking the process cap by cat /proc/pid/status | grep Cap, I found

CapInh: 0000000000000000
CapPrm: 0000000000000400
CapEff: 0000000000000400
CapBnd: 000001ffffffffff
CapAmb: 0000000000000000

Questions: 1. But when I still got the error binding: Permission denied 2. How do know which bit correspond to which cap in such output 0000000000000400?