Update SQL Query with populated variables from AJAX functions over multiple PHP Pages

i try to get help with that question.

All in all Q: It doesnt Update my DB entry like this Step by Step Order how i think it could be done.

its a bit difficult to explain, but i try to explain it step by step with minimal and readable Code. I use the original code, its hard to convert it in reproducible Examples.

A.1 Page ma_aktuelle_ReadOut.php There is a php Part

 <?php echo "<a href='ma_Testende.php?TestergebnisID=&TestaufstellungID=". $row['TestaufstellungID']."&TesterID=".$row['TesterID']."' title='Test stoppen' data-toggle='tooltip' class='stoppen'>   <span class='glyphicon glyphicon-stop'></span></a>";
?>

When i click this link the following javascript function is called and ask me "really stop?"

<script language="JavaScript" type="text/javascript">
$(document).ready(function(){
  $("a.stoppen").click(function(e){
   if(!confirm('Wirklich stoppen?')){
    e.preventDefault();
    $('.alert').show()
    return false;
    }
    return true;
            });
        });
</script>
<style>
 .alert {
  display: none;
    }
</style>

When i cklick "yes" it opens the second Page.

A 2 Page ma_Testende.php On this Page are 2 AJAX JS Functions. The first Ajax is asking for "Datum" via type:get from the following next page and wait till success (see Page B 3):

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js">

/* function to get Stoptime for Cycle from DB.TesterCycleCount zu erhalten  */ 
$(document).ready(async function(){
var Datum;
var TesterID = "<?php echo $_GET['TesterID']; ?>"; /* value from TesterID */ 
await $.ajax({ /* First Ajax function */
            url: 'ma_get-TesterID_Testende.php',
            type: 'get', 
            data: {TesterID:TesterID}, 
            dataType: 'json',
            success:function(response){ 
                var CID = response['CID'];
                Datum = response['Datum'];
                console.log(response);
            },
             error: function(jqxhtt, status, exception) {
                 console.log(exception);
         alert('Exception:', exception)
            }
        });
console.log();
        var TestaufstellungID = "<?php echo $_GET['TestaufstellungID']; ?>";
         $.ajax({ /* Second Ajax function */
            url: 'ma_TestendeSQL.php',
            type: 'get', 
            data: {TestaufstellungID:TestaufstellungID, Datum: Datum}, 
            dataType: 'json',
            success:function(data){ 
            alert('Successfully called');
     },
     error: function(jqxhr, status, exception) {
         console.log(exception);
         alert('Exception:', exception)
            }
        });
        });
</script>

B 3 Page ma_get-TesterID_Testende.php

<?php
$cinfo = array(
    "Database" => $database,
    "UID" => $username,
    "PWD" => $password
);
$conn = sqlsrv_connect($server, $cinfo);
                $sqlreadZeit = "Select TOP 1 CID,Datum from DB.dbo.TesterCycleCount where TesterID = '".$_GET['TesterID']."' order by Datum DESC";
                $result1 = sqlsrv_query($conn, $sqlreadZeit);
                $zeiten_arr = array();
                while ($row = sqlsrv_fetch_array($result1, SQLSRV_FETCH_ASSOC)) {
                $CID = $row['CID'];
                $Datum = $row['Datum']->format('d.m.Y h:m:s');
                $zeiten_arr[] = array("CID" => $CID, "Datum" => $Datum);
                                }
    header('Content-type: application/json');
  echo json_encode($zeiten_arr); 
?>

Back with the "Datum" the second AJAX is called (see Page A 2) With the "Datum" and "TestaufstellungID" as variable it should be call the next Page and Update the DB entry with the populated variablles.

B. 4 Page ma_TestendeSQL.php

<?php
$cinfo = array(
    "Database" => $database,
    "UID" => $username,
    "PWD" => $password
);
$conn = sqlsrv_connect($server, $cinfo);

$TestaufstellungID = $_GET['TestaufstellungID'];
$Testende= $_GET['Datum'];
$Testdatum = date('Y-d-m');

$stop = $connection->prepare("WITH UpdateTestende AS (
  SELECT TOP 1  * from DB.dbo.Testergebnisse 
  WHERE TestaufstellungID = :TestaufstellungID
  ORDER BY TestergebnisID DESC 
)
update UpdateTestende 
set Testende = :Testende,
Datum = :Testdatum");
$stop->execute(array(':TestaufstellungID' => $TestaufstellungID, ':Testdatum' => $Testdatum, ':Testende' => $Testende));

    header('Content-type: application/json');
?>

The php variable $Testende get the populated "Datum" from the Ajax functions. All in all at the end it should be Update, when i click on the link the ( Page A 1) my DB entry with the populated "Datum" which i get from the first Ajax call ( Page A 2 ) from the SQL Query ( Page B 3) back to the second AJAX Call ( Page A 2 ) than with the data: {TestaufstellungID:TestaufstellungID, Datum: Datum} to the last page ( Page B 4)

But it doesnt Update my DB entry like this Step by Step Order how i think it could be done.

Encapsulated is the SQL-Code working fine. With the Code header('Content-type: application/json'); the browser tell me the following when i click on the link from ( Page A 1 )

SyntaxError: JSON.parse: unexpected character at line 1 column 1 of the JSON data

Thats why i posted all the Step i think on one point the variables are not passed right to the next page or they are empty becasue the code is not executed in the right order Server/Client PHP/JS or Asynchronous problem... The console.log tell me nothing. At the moment i have no idea where to start with the debugging?

Hope someone can help me. thx

Edit: iam pretty sure the ajax call is empty, but i dont see it in which step the values getting empty

from Update SQL Query with populated variables from AJAX functions over multiple PHP Pages