Post data using php

I’m new in API development, I made an API to fetch and store data, I can fetch data without any problem, but everything changes when I try to store data, when I send the data to store it returns [{"success":"0"}]. In the beginning it worked well, it accepted to store data, but suddenly everything changed. I’ve tried everything, compare new code with the old, change the code, tables, but even so it always returns [{"success":"0"}] after comparing both (old and new) code I couldn’t see much difference. What could I be doing wrong?

Insert data:

function insertloin()
{
    if(isset($_POST["loincode"]))
    {
        $form_data = array(
            ':loincode'     =>  $_POST["loincode"],
            ':code'     =>  $_POST["code"],
            ':specie'       =>  $_POST["specie"],
            ':grade'        =>  $_POST["grade"],
            ':vesselname'       =>  $_POST["vesselname"],
            ':type'     =>  $_POST["type"],
            ':productformat'        =>  $_POST["productformat"],
            ':dateprocessed'        =>  $_POST["dateprocessed"],
            ':datebb'       =>  $_POST["datebb"],
            ':projectcode'      =>  $_POST["projectcode"],
            ':netweight'        =>  $_POST["netweight"],
            ':producttype'      =>  $_POST["producttype"],
            ':oldoc'        =>  $_POST["oldoc"]
            
        );
        $query = "
        INSERT INTO loins 
        (loincode, code, specie, grade, vesselname, type, productformat, dateprocessed, datebb, projectcode, netweight, producttype, oldoc) VALUES 
        (:loincode, :code, :specie, :grade, :vesselname, :type, :productformat, :dateprocessed, :datebb, :projectcode, :netweight, :producttype, :oldoc)
        ";
        $statement = $this->connect->prepare($query);
        if($statement->execute($form_data))
        {
            $data[] = array(
                'success'   =>  '1'
            );
        }
        else
        {
            $data[] = array(
                'success'   =>  '0'
            );
        }
    }
    else
    {
        $data[] = array(
            'success'   =>  '0'
        );
    }
    return $data;
}

Test:

    if($_GET["action"] == 'insertloin')
{
    $data = $api_object->insertloin();
}

Action:

    if(isset($_POST["action"]))
{
    if($_POST["action"] == 'insertloin')
    {
        $form_data = array(
                'loincode'      =>  $_POST["loincode"],
                'code'      =>  $_POST["code"],
                'specie'        =>  $_POST["specie"],
                'grade'     =>  $_POST["grade"],
                'vesselname'        =>  $_POST["vesselname"],
                'type'      =>  $_POST["type"],
                'productformat'     =>  $_POST["productformat"],
                'dateprocessed'     =>  $_POST["dateprocessed"],
                'datebb'        =>  $_POST["datebb"],
                'projectcode'       =>  $_POST["projectcode"],
                'netweight'     =>  $_POST["netweight"],
                'producttype'       =>  $_POST["producttype"],
                'oldoc'     =>  $_POST["oldoc"]
        );
        $api_url = "http://192.168.85.160/API/v2/api/test_api.php?action=insertloin";
        
        $client = curl_init($api_url);
        curl_setopt($client, CURLOPT_POST, true);
        curl_setopt($client, CURLOPT_POSTFIELDS, $form_data);
        curl_setopt($client, CURLOPT_RETURNTRANSFER, true);
        $response = curl_exec($client);
        curl_close($client);
        $result = json_decode($response, true);
        foreach($result as $keys => $values)
        {
            if($result[$keys]['success'] == '1')
            {
                echo 'insert';
            }
            else
            {
                echo 'error';
            }
        }
    }

Please, help me find the bug.
Kind regards,
Abd