Post ArrayList to PHP and add it to MySQL database - php

Question

I am creating an app similar to those from online stores
I did an ArrayList for products added to the shopping cart.
How I must do to send this into my PHP script and add this to MySQL database.
I tried return count of my ArrayList elements, but I can't.
This is PHP code:
<?php
$postedArray = $_POST["arrayToPOST"];
$response = array();
if(isset($postedArray))
{
$count = count($postedArray);
$response["Count"] = $count;
$response["postedArray"] = $postedArray;
}
else
{
$response["Count"] = 0;
$response["postedArray"] = "ERROR ON POST";
}
echo json_encode($response);
?>
This is my function in Android app:
val arrayList: ArrayList<String> = ArrayList<String>()
arrayList.add("First value")
arrayList.add("Second value")
arrayList.add("Third value")
val gson = GsonBuilder()
.setLenient()
.create()
val retrofit = Retrofit.Builder()
.addConverterFactory(GsonConverterFactory.create(gson))
.baseUrl("http://192.168.100.11/")
.build()
val webAPIInterface = retrofit.create(WebAPIInterface::class.java)
var call = webAPIInterface.postData(arrayList)
call.enqueue(object : Callback<ResponsePOJO> {
override fun onFailure(call: Call<ResponsePOJO>?, t: Throwable?) {
Log.e("MainActivity", "Retrofit 2 ERROR: "+t.toString())
}
override fun onResponse(call: Call<ResponsePOJO>?, response: Response<ResponsePOJO>?)
{
Log.v("MainActivity", "RESPONSE: "+response!!.body().toString())
if(response!!.isSuccessful)
{
Log.v("MainActivity", "Response is successful")
Log.v("MainActivity", "")
}
else
{
Log.e("MainActivity", "Response isnt successful")
}
}
})
I looking for solution in internet, but I found nothing.
Please help !