Untested Switching Concept

#include <ESP8266WiFi.h>
#include <WiFiClient.h>
#include <ESP8266WebServer.h>
#include <ESP8266HTTPClient.h>

// SSID and Password for AP mode
const char *ssid = "node_middle1";
const char *password = "a12345678";

// SSID and Password for other ESP network
const char *nextSSID = "main_node";
const char *nextPassword = "a12345678";

// Check if already get data from last node
int connectionMadeWithLastNode = 0;

// Check if configClientMode() was already called
int clientModeConfigured = 0;

// Fixed IP in network on AP mode
IPAddress apIP(192, 168, 4, 1);

ESP8266WebServer server(80);

void response();
void configAPMode();
void configClientMode();
void sendMessage();

void setup() {
  Serial.begin(115200);
  configAPMode();
}

void loop() {
  if(connectionMadeWithLastNode == 0){
    server.handleClient();
  } else {
    if(clientModeConfigured == 0) {
      configClientMode();
    } else{
      sendMessage();
    }
  }
}

void response() {
  Serial.print("MENSAGEM DO ULTIMO NÓ: ");
  Serial.println(server.arg("plain"));
  server.send(200);
  connectionMadeWithLastNode = 1;
}

void configAPMode() {
  WiFi.mode(WIFI_AP_STA);
  WiFi.softAP(ssid, password);

  server.on("/", response);
  server.begin();
}

void configClientMode() {
  WiFi.softAPdisconnect();
  WiFi.begin(nextSSID, nextPassword);
  clientModeConfigured = 1;
  Serial.println("CLIENT MODE");
}

void sendMessage(){
  if (WiFi.status() == WL_CONNECTED){
    HTTPClient http;
    http.begin("http://192.168.4.1");
    http.addHeader("Content-Type", "application/json");
    int httpCode = http.POST("{\"Value\": 200}");
    Serial.print("HTTP Code: ");
    Serial.println(httpCode);

    http.end();
  }
}