How do I use my local IP address like as my api in http.begin()

#include <wifi.h>
#include <httpclient.h>

const char* ssid = "My-SSID";
const char* password = "My-Password";

IPAddress ip;
IPAddress local_IP(192, 168, 1, 88);
IPAddress gateway(192, 168, 1, 1);
IPAddress subnet(255, 255, 0, 0);
IPAddress primaryDNS(8, 8, 8, 8); //optional
IPAddress secondaryDNS(8, 8, 4, 4); //optional

void setup() {

Serial.begin(115200);
HTTPClient http;
Serial.println("Try Connecting to ");
Serial.println(ssid);

if (!WiFi.config(local_IP, gateway, subnet, primaryDNS, secondaryDNS))
{
Serial.println("STA Failed to configure");
}

Serial.print("Connecting to ");
Serial.println(ssid);
WiFi.begin(ssid, password);

while (WiFi.status() != WL_CONNECTED) {
delay(1000);
}
Serial.println("");
Serial.println("WiFi connected successfully");
Serial.print("Got IP: ");
ip = WiFi.localIP();
Serial.println(ip); //Show ESP32 IP on serial

Serial.println("HTTP server started");
delay(100);

http.begin("http://ip.sms.ir/SendMessage.ashx?user=[user]&pass=[pass]&text=[text]&to=[to]&lineNo=[lineNo]"); //works fine also works fine in a browser.
http.begin("http://192.168.1.88:8081"); //Not Working Here
(but in a browser http://192.168.1.88:8081 works fine)

int httpCode = http.GET();

if (httpCode > 0)
{
String payload = http.getString();
Serial.println(httpCode);
Serial.println(payload);
}

else
{
Serial.println("Error on HTTP request");
}

http.end(); //Free the resources

}
void loop() {

}