I solved it by changing https to http.
Also added string data "123" (any number), otherwise new position is not opened, server responds with confirmation of previously opened trade.
Code:
// ------------------------- Trade4me/binary.com API
  
function main()
{
  char ip_str[100]; // just a long empty string
  int id = http_post("http://trade4.me/order.php?username=Fiber100&password=Awainter1t&asset=EUR/USD&direction=UP&expiry=1&amount=10&rand=","123");
  if(!id) return;
  while(!http_status(id)) {
    if(!wait(100)) return; // wait for the server to reply
    printf(".");
  }  if(http_status(id) > 0) { //transfer successful?
    http_result(id,ip_str,100);   //get the replied IP
    printf("n%s",ip_str);
  } else
    printf("nError during transfer!");
  http_free(id); //always clean up the id!
}

Only thing I couldn't resolve how to insert variables into http for instrument, direction, duration and stake.
Error in 'line 11:
Can not convert '' to 'ARRAY'
Code:
// ------------------------- Trade4me/binary.com API
  
function main()
{
  char ip_str[100]; // just a long empty string
  string Instr = "EUR/USD";
  string Direction = "UP";
  string Exp = "1";
  string Size = "10";
  int id = http_post("http://trade4.me/order.php?username=Fiber100&password=Awainter1t&asset="+Instr+"&direction="+Direction+"&expiry="+Exp+"&amount="+Size+"&rand=","123");
  if(!id) return;
  while(!http_status(id)) {
    if(!wait(100)) return; // wait for the server to reply
    printf(".");
  }  if(http_status(id) > 0) { //transfer successful?
    http_result(id,ip_str,100);   //get the replied IP
    printf("n%s",ip_str);
  } else
    printf("nError during transfer!");
  http_free(id); //always clean up the id!
}