Json to php array Arrangement

$data='{
    "Body":{
        "stkCallback":{
            "MerchantRequestID":"26642-2152252-1",
            "CheckoutRequestID":"ws_CO_DMZ_240346011_09022019093008828",
            "ResultCode":0,
            "ResultDesc":"The service request is processed successfully.",
            "CallbackMetadata":{
                "Item":[
                    {"Name":"Amount","Value":10.00},
                    {"Name":"MpesaReceiptNumber","Value":"NB92QAMYN2"},
                    {"Name":"Balance"},
                    {"Name":"TransactionDate","Value":20190209093032},
                    {"Name":"PhoneNumber","Value":254723513144}
                ]
            }
        }
    }
}';

$number=false;

/* use `json_decode` to make the data usable */
$json=json_decode( $data );

/* find the array of items */
$items=$json->Body->stkCallback->CallbackMetadata->Item;

/* loop through the array until you find the one you want. */
foreach( $items as $obj ){
    if( $obj->Name=='PhoneNumber' )$number=$obj->Value;
}
/* do something with the number... */
if( $number )echo $number;

In the question you embed the number in the sql - you should consider using a prepared statement instead to avoid sql injection... like this perhaps

$number=false;


$json=json_decode( $data );

$items=$json->Body->stkCallback->CallbackMetadata->Item;
$code=$json->Body->stkCallback->ResultCode;

foreach( $items as $obj ){
    if( $obj->Name=='PhoneNumber' )$number=$obj->Value;
}

if( $number ){
    $sql='update `pay` set `resultcode`=? where `uniqs`=?';
    $stmt=$db->prepare($sql);
    $stmt->bind_param( 'is', $code, $number );
    $stmt->execute();
}

That is because $json['Body']['stkCallback']["CallbackMetadata"]['Item'] is an array filled with objects ( with Name and Value).

Therefore you need to traverse it and fetch item whose Name === PhoneNumber:

foreach ($json['Body']['stkCallback']["CallbackMetadata"]['Item'] as $item) {
    if ($item['Name'] === 'PhoneNumber') {
        $PhoneNumber = $item['Value'];
    }
}

Let me know if it worked. Of course, before saving it to the DB you should check if $PhoneNumber is actually filled.

• You need to convert your JSON object into a PHP Object first.
• Then, as your Item is an array, you'll need to loop over it to obtain your required field i.e. PhoneNumber.

So, following is an illustration of the same -

<?php
  $jsonObj = '{
    "Body":{
        "stkCallback":{
            "MerchantRequestID":"26642-2152252-1",
            "CheckoutRequestID":"ws_CO_DMZ_240346011_09022019093008828",
            "ResultCode":0,
            "ResultDesc":"The service request is processed successfully.",
            "CallbackMetadata":{
                "Item":[
                    {"Name":"Amount","Value":10.00},
                    {"Name":"MpesaReceiptNumber","Value":"NB92QAMYN2"},
                    {"Name":"Balance"},
                    {"Name":"TransactionDate","Value":20190209093032},
                    {"Name":"PhoneNumber","Value":254723513144}
                ]
            }
        }
    }
  }';

  // json_decode your json array here
  $phpObj = json_decode($jsonObj, true);

  // get items array from the main object
  $items = $phpObj['Body']['stkCallback']['CallbackMetadata']['Item'];

  // loop over items to get desired field
  foreach($items as $obj) {
    if($obj['Name'] === 'PhoneNumber')
        $PhoneNumber = $obj['Value'];
  }
  echo $PhoneNumber;
?>