I am using ESP32 Arduino websocket using WifiMulti. There is example using Static IP ((https://github.com/espressif/arduino-esp32/blob/master/libraries/WiFi/examples/WiFiClientStaticIP/WiFiClientStaticIP.ino) I copied below:
#include <WiFi.h>

const char* ssid = "your_network_name";
const char* password = "your_network_password";
const char* host = "example.com";
const char* url = "/index.html";

IPAddress local_IP(192, 168, 31, 115);
IPAddress gateway(192, 168, 31, 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);

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(500);
Serial.print(".");
}

Serial.println("");
Serial.println("WiFi connected!");
Serial.print("IP address: ");
Serial.println(WiFi.localIP());
Serial.print("ESP Mac Address: ");
Serial.println(WiFi.macAddress());
Serial.print("Subnet Mask: ");
Serial.println(WiFi.subnetMask());
Serial.print("Gateway IP: ");
Serial.println(WiFi.gatewayIP());
Serial.print("DNS: ");
Serial.println(WiFi.dnsIP());
}
/******************************/
My problem is with my project using WiFiMulti which is not supporting Static IP
WiFiMulti.addAP(SSID, pass);
Serial.print("Wait for WiFi... ");
while(WiFiMulti.run() != WL_CONNECTED) {
Serial.print(". ");
delay(500);
}