ESP32 records corrupt WAV file audio

I am using SeedStudio ESP32 Xiao Sense to record multiple samples of audio at once. I modified the sample code to do so. However, for some reason the header is corrupted(not sure for other parts) and the file will not play.

Below is the code I modified. I can't find the error and don't know how to proceed further.

Link to audio files: Google drive folder for audio samples recorded.

#include "ESP_I2S.h"
#include "FS.h"
#include "SD.h"

void record(uint8_t wav_buffer, size_t wav_size, int i);
void save(uint8_t* wav_buffer, size_t wav_size, int i);

void setup() {

  Serial.begin(115200);
  while (!Serial) {
    delay(10);
  }

  I2SClass i2s;

  uint8_t *wav_buffer;
  size_t wav_size;

  Serial.println("Initializing I2S bus...");

  i2s.setPinsPdmRx(42, 41);

  for(int i=0; i<5;i++){
    record(i2s, wav_buffer, wav_size, i);
  }

  Serial.println("Application complete.");
}

void record(I2SClass i2s, uint8_t* wav_buffer, size_t wav_size, int i){

  // start I2S at 16 kHz with 16-bits per sample
  if (!i2s.begin(I2S_MODE_PDM_RX, 16000, I2S_DATA_BIT_WIDTH_16BIT, I2S_SLOT_MODE_MONO)) {
    Serial.println("Failed to initialize I2S!");
    while (1); // do nothing
  }

  Serial.println("I2S bus initialized.");
  // Serial.println(wav_size);
  wav_buffer = i2s.recordWAV(5, &wav_size);

  // Serial.println(wav_size);
  free(wav_buffer);
  
  // Serial.println("Block END\n");
  save(wav_buffer, wav_size, i);
  }

void save(uint8_t* wav_buffer, size_t wav_size, int i){

  Serial.println("Initializing SD card...");
  if(!SD.begin(21)){
    Serial.println("Failed to mount SD Card!");
    while (1) ;
  }
  Serial.println("SD card initialized.");

  String file_name = "/audio_"+String(i)+".wav";
  // Create a file on the SD card
  File file = SD.open(file_name, FILE_WRITE);
  if (!file) {
    Serial.println("Failed to open file for writing!");
    return;
  }

  Serial.println("Writing audio data to file...");

  // Write the audio data to the file
  if (file.write(wav_buffer, wav_size) != wav_size) {
    Serial.println("Failed to write audio data to file!");
    return;
  }

  file.close();
}

void loop() {
  delay(1000);
  Serial.printf(".");
}