Code
/******************************************
 *
 * This example works for both Industrial and STEM users.
 *
 * Developed by Jose Garcia, https://github.com/jotathebest/
 *
 * ****************************************/

/****************************************
 * Include Libraries
 ****************************************/
#include "UbidotsEsp32Mqtt.h"

/****************************************
 * Define Constants
 ****************************************/
const char *UBIDOTS_TOKEN = "XXXXXXXXXXXXXXXXXX";  // Put here your Ubidots TOKEN
const char *WIFI_SSID = "Jimmy";      // Put here your Wi-Fi SSID
const char *WIFI_PASS = "12345678";      // Put here your Wi-Fi password
const char *DEVICE_LABEL = "variable1";   // Put here your Device label to which data  will be published
const char *VARIABLE_LABEL = "variable2"; // Put here your Variable label to which data  will be published

const int PUBLISH_FREQUENCY = 5000; // Update rate in milliseconds

unsigned long timer;
uint8_t analogPin = 34; // Pin used to read data from GPIO34 ADC_CH6.

Ubidots ubidots(UBIDOTS_TOKEN);

/****************************************
 * Auxiliar Functions
 ****************************************/

void callback(char *topic, byte *payload, unsigned int length)
{
  Serial.print("Message arrived [");
  Serial.print(topic);
  Serial.print("] ");
  for (int i = 0; i < length; i++)
  {
    Serial.print((char)payload[i]);
  }
  Serial.println();
}

/****************************************
 * Main Functions
 ****************************************/

void setup()
{
  // put your setup code here, to run once:
  Serial.begin(115200);
  // ubidots.setDebug(true);  // uncomment this to make debug messages available
  ubidots.connectToWifi(WIFI_SSID, WIFI_PASS);
  ubidots.setCallback(callback);
  ubidots.setup();
  ubidots.reconnect();

  timer = millis();
}

void loop()
{
  // put your main code here, to run repeatedly:
  if (!ubidots.connected())
  {
    ubidots.reconnect();
  }
  if (abs(millis() - timer) > PUBLISH_FREQUENCY) // triggers the routine every 5 seconds
  {
    float value = analogRead(analogPin);
    ubidots.add(VARIABLE_LABEL, value); // Insert your variable Labels and the value to be sent
    ubidots.publish(DEVICE_LABEL);
    timer = millis();
  }
  ubidots.loop();
}





ERROR
C:\Users\andre\AppData\Local\Temp\.arduinoIDE-unsaved2023816-4184-hht6li.sfnx4\sketch_sep16a\sketch_sep16a.ino: In function 'void loop()':
C:\Users\andre\AppData\Local\Temp\.arduinoIDE-unsaved2023816-4184-hht6li.sfnx4\sketch_sep16a\sketch_sep16a.ino:70:27: error: call of overloaded 'abs(long unsigned int)' is ambiguous
   if (abs(millis() - timer) > PUBLISH_FREQUENCY) // triggers the routine every 5 seconds
                           ^
In file included from c:\users\andre\appdata\local\arduino15\packages\esp32\tools\xtensa-esp32-elf-gcc\esp-2021r2-patch5-8.4.0\xtensa-esp32-elf\include\c++\8.4.0\cstdlib:75,
                 from c:\users\andre\appdata\local\arduino15\packages\esp32\tools\xtensa-esp32-elf-gcc\esp-2021r2-patch5-8.4.0\xtensa-esp32-elf\include\c++\8.4.0\stdlib.h:36,
                 from C:\Users\andre\AppData\Local\Arduino15\packages\esp32\hardware\esp32\2.0.13/tools/sdk/esp32/include/newlib/platform_include/assert.h:21,
                 from c:\users\andre\appdata\local\arduino15\packages\esp32\tools\xtensa-esp32-elf-gcc\esp-2021r2-patch5-8.4.0\xtensa-esp32-elf\sys-include\sys\reent.h:503,
                 from C:\Users\andre\AppData\Local\Arduino15\packages\esp32\hardware\esp32\2.0.13/tools/sdk/esp32/include/newlib/platform_include/sys/reent.h:17,
                 from c:\users\andre\appdata\local\arduino15\packages\esp32\tools\xtensa-esp32-elf-gcc\esp-2021r2-patch5-8.4.0\xtensa-esp32-elf\sys-include\stdio.h:60,
                 from C:\Users\andre\AppData\Local\Arduino15\packages\esp32\hardware\esp32\2.0.13\cores\esp32/Arduino.h:27,
                 from C:\Users\andre\AppData\Local\Temp\arduino\sketches\9182674C95D90AE77C2DEBA2E2882BC5\sketch\sketch_sep16a.ino.cpp:1:
c:\users\andre\appdata\local\arduino15\packages\esp32\tools\xtensa-esp32-elf-gcc\esp-2021r2-patch5-8.4.0\xtensa-esp32-elf\sys-include\stdlib.h:74:5: note: candidate: 'int abs(int)'
 int abs (int);
     ^~~
In file included from c:\users\andre\appdata\local\arduino15\packages\esp32\tools\xtensa-esp32-elf-gcc\esp-2021r2-patch5-8.4.0\xtensa-esp32-elf\include\c++\8.4.0\cstdlib:77,
                 from c:\users\andre\appdata\local\arduino15\packages\esp32\tools\xtensa-esp32-elf-gcc\esp-2021r2-patch5-8.4.0\xtensa-esp32-elf\include\c++\8.4.0\stdlib.h:36,
                 from C:\Users\andre\AppData\Local\Arduino15\packages\esp32\hardware\esp32\2.0.13/tools/sdk/esp32/include/newlib/platform_include/assert.h:21,
                 from c:\users\andre\appdata\local\arduino15\packages\esp32\tools\xtensa-esp32-elf-gcc\esp-2021r2-patch5-8.4.0\xtensa-esp32-elf\sys-include\sys\reent.h:503,
                 from C:\Users\andre\AppData\Local\Arduino15\packages\esp32\hardware\esp32\2.0.13/tools/sdk/esp32/include/newlib/platform_include/sys/reent.h:17,
                 from c:\users\andre\appdata\local\arduino15\packages\esp32\tools\xtensa-esp32-elf-gcc\esp-2021r2-patch5-8.4.0\xtensa-esp32-elf\sys-include\stdio.h:60,
                 from C:\Users\andre\AppData\Local\Arduino15\packages\esp32\hardware\esp32\2.0.13\cores\esp32/Arduino.h:27,
                 from C:\Users\andre\AppData\Local\Temp\arduino\sketches\9182674C95D90AE77C2DEBA2E2882BC5\sketch\sketch_sep16a.ino.cpp:1:
c:\users\andre\appdata\local\arduino15\packages\esp32\tools\xtensa-esp32-elf-gcc\esp-2021r2-patch5-8.4.0\xtensa-esp32-elf\include\c++\8.4.0\bits\std_abs.h:78:3: note: candidate: 'constexpr long double std::abs(long double)'
   abs(long double __x)
   ^~~
c:\users\andre\appdata\local\arduino15\packages\esp32\tools\xtensa-esp32-elf-gcc\esp-2021r2-patch5-8.4.0\xtensa-esp32-elf\include\c++\8.4.0\bits\std_abs.h:74:3: note: candidate: 'constexpr float std::abs(float)'
   abs(float __x)
   ^~~
c:\users\andre\appdata\local\arduino15\packages\esp32\tools\xtensa-esp32-elf-gcc\esp-2021r2-patch5-8.4.0\xtensa-esp32-elf\include\c++\8.4.0\bits\std_abs.h:70:3: note: candidate: 'constexpr double std::abs(double)'
   abs(double __x)
   ^~~
c:\users\andre\appdata\local\arduino15\packages\esp32\tools\xtensa-esp32-elf-gcc\esp-2021r2-patch5-8.4.0\xtensa-esp32-elf\include\c++\8.4.0\bits\std_abs.h:61:3: note: candidate: 'long long int std::abs(long long int)'
   abs(long long __x) { return __builtin_llabs (__x); }
   ^~~
c:\users\andre\appdata\local\arduino15\packages\esp32\tools\xtensa-esp32-elf-gcc\esp-2021r2-patch5-8.4.0\xtensa-esp32-elf\include\c++\8.4.0\bits\std_abs.h:56:3: note: candidate: 'long int std::abs(long int)'
   abs(long __i) { return __builtin_labs(__i); }
   ^~~

exit status 1

Compilation error: call of overloaded 'abs(long unsigned int)' is ambiguous