central connection error

Hi Everyone.

IDE : Vs Code

SDK : nrfConnect SDK

I have tried to connect peripheral device based on address. User gives input , address of ble device and based on that, I would start ble connection request.

I was successfull to connect, If I call below api inside scan_response function. But, If I wait for user input and call for same api, the connection callback throws error -2 and sometimes by luck it connects.

I suppose central can only start connection request while peripheral is still adversting.

Now, I wish to know how to start a connection at my will, and make sure it connects. Also, what should be min max intervals, so that connection request would wait for sometime.

tm_bool_t bt_connect(const bt_addr_le_t *addr,struct bt_conn **conn)
{ 
  int err;
  struct bt_le_conn_param param2,*param;
  param = BT_LE_CONN_PARAM_DEFAULT;
//   param->latency = 400;
//   param->timeout = 400;
param2.interval_max = 0x28;
param2.interval_min = 0x18;
param2.latency = 10;
param2.timeout = 400;

 
  err = bt_conn_le_create(addr, BT_CONN_LE_CREATE_CONN,
      &param2,  conn);
  if (err) 
  {
    sprintf(tx_buf,"Create conn failed (err %d)\n", err);
    DPRINTF(tx_buf); /* Debug print in uart */
    return FALSE;
    
  }
  sprintf(tx_buf,"Create conn success (err %d)\n", err);
    DPRINTF(tx_buf);
  return TRUE;

}

Edit:

If connection timeout's I get error 2 inside connection_callback;

After that If I try  again to connect using same address, I get -EINVAL(22) response  and connection doesn't create. 

if (bt_conn_exists_le(BT_ID_DEFAULT, peer)) {
		return -EINVAL;
	}

how to prevent this happening again?