Not working for Big Database

I got a database with 738.600 Rows and 20 ( + 1 uniqueID) columns.
This is my app.js and the error is "invalid JSON response".
If i manually set the LIMIT in the simple function from ssp.class.php to e.g. 0, 10000 i get data displayed, non paginated and non filterable, 10000 on one site.

If i manually open my webiste + getData.php i see blank page.

$(document).ready(function() {
  $('#ItemList').DataTable({
    "processing": true,
    "serverSide": true,
    "paging": true,
    "ajax": {
      "url": '../getData.php',
      "dataSrc": 'data', //data because ssp.class.php adds data to it
      "type": 'POST'
    },
    "columns": [
        { "data": 'Held' },
        { "data": 'Waffe' },
        { "data": 'Schild' },
        { "data": 'Ring' },
        { "data": 'Amulett' },
        { "data": 'Mantel' },
        { "data": 'Off' },
        { "data": 'OffT' },
        { "data": 'Def' },
        { "data": 'DefT' },
        { "data": 'Hybrid' },
        { "data": 'HybridT' },
        { "data": 'DefA' },
        { "data": 'DefAT' },
        { "data": 'OffA' },
        { "data": 'OffAT1' },
        { "data": 'OffAT2' },
        { "data": 'HybridA' },
        { "data": 'HybridAT1' },
        { "data": 'HybridAT2' },
        { "data": 'ExtraTruppen' }
      ]
  });
});

And here my simple getData.php

<?php
    require 'ssp.class.php';

    $table = 'TABLENAME';
    $primaryKey = 'ID';
    $columns = array(
        array( 'db' => 'Held', 'dt' => 'Held' ),
        array( 'db' => 'Waffe', 'dt' => 'Waffe' ),
        array( 'db' => 'Schild', 'dt' => 'Schild' ),
        array( 'db' => 'Ring', 'dt' => 'Ring' ),
        array( 'db' => 'Amulett', 'dt' => 'Amulett' ),
        array( 'db' => 'Mantel', 'dt' => 'Mantel' ),
        array( 'db' => 'Off', 'dt' => 'Off' ),
        array( 'db' => 'OffT', 'dt' => 'OffT' ),
        array( 'db' => 'Def', 'dt' => 'Def' ),
        array( 'db' => 'DefT', 'dt' => 'DefT' ),
        array( 'db' => 'Hybrid', 'dt' => 'Hybrid' ),
        array( 'db' => 'HybridT', 'dt' => 'HybridT' ),
        array( 'db' => 'DefA', 'dt' => 'DefA' ),
        array( 'db' => 'DefAT', 'dt' => 'DefAT' ),
        array( 'db' => 'OffA', 'dt' => 'OffA' ),
        array( 'db' => 'OffAT1', 'dt' => 'OffAT1' ),
        array( 'db' => 'OffAT2', 'dt' => 'OffAT2' ),
        array( 'db' => 'HybridA', 'dt' => 'HybridA' ),
        array( 'db' => 'HybridAT1', 'dt' => 'HybridAT1' ),
        array( 'db' => 'HybridAT2', 'dt' => 'HybridAT2' ),
        array( 'db' => 'ExtraTruppen', 'dt' => 'ExtraTruppen' )
    );

    $sql_details = array(
        'user' => 'user',
        'pass' => 'pass',
        'db'   => 'DATABASE',
        'host' => 'localhost'
    );
    
    echo json_encode(
        SSP::simple( $_GET, $sql_details, $table, $primaryKey, $columns )
    );
?>