sql server - how to alter table in ms sql server2014 using php

error I am using ms sql database for the first time and I am trying to make an update on the table using php. these are the codes that I used for the update. it says there's an error "Undefined index: cust_id "

$serverName = "kwe-PC\SQLEXPRESS";
$connectionInfo = array("Database" => "customerdb", "UID" => "dbadmin", "PWD" => "kwe");
$conn = sqlsrv_connect($serverName, $connectionInfo);

if ($conn === false) {
    die(print_r(sqlsrv_errors(), true));
}
//declare the SQL statement that will query the database
$query = "SELECT * FROM Customer_Details WHERE Rec_No=".$_POST['id'];

//execute the SQL query and return records
$result = sqlsrv_query($conn, $query)
        or die(print_r(sqlsrv_errors(), true));
//Show results in table


$o = '';
while ($record = sqlsrv_fetch_array($result)) {
	$street1 = $record['street'];
	$o .='';
    $o .= '';
    $o .= '';
    $o .= '';
    $o .="";
    $o .= '';

	$o .= '';
    /*$o .='';*/
	$o .='';
	$o .='';
    $o .='';
    $o .='';
    $o .='';
    $o .='';
	$o .='';
	$o .='';

	$o .='';
	$o .='';
	$o .='';
	$o .='';
	$o .='';
	$o .='';
    $o .='';
	$o .='';
	$o .='';
	$o .='';

	$o .='';
	$o .='';
	$o .='';
	$o .='';
	$o .='';
	$o .='';
	$o .='';
	$o .='';
	$o .='';
	$o .='';

	$o .='';
	}

$o .= '
REC NO.: 
CUSTOMER ID: 
CUSTOMER NAME: 
SEC-REGISTERED NAME: 
TIN NUMBER: 
STORE TYPE: 
ORGANIZATION AND BUSINESS:
SIZE OF BUSINESS: 
SELLER ID: 
DATE OF ESTABLISHMENT: 
' . date('F d, Y', strtotime($record ['Date of Establishment'])) . '
ADDRESS(Headquarters): 
 
TELEPHONE# / FAX: 
PAYMENT TERMS: 
SHIPPING INSTRUCTIONS: 
NUMBER OF DOORS: 
NUMBER OF WAREHOUSES: 
CONTACT PERSONNEL:
OWNER: 
PURCHASER/S: 
ACCOUNTING HEAD: 
WAREHOUSE HEAD: 
OTHER PERSONNEL: 
TERMS AND DISCOUNTS:
PAYMENT TERMS: 
COLLECTION SCHEDULE:
DISCOUNT: 
BUSINESS GOALS:
VOLUME:
CSL:
MERCHANDISING:
ASSORTMENT:
VEHICLE:
PRICING:
DISTRIBUTION:
MARGIN:
STRATEGIES:
PRICE:
PEOPLE:
PROMOTION:
PRODUCT:
CATMAN ENROLLMENT:
POLICIES:
REPLENISHMENT ORDERS:
ASSORTMENT/MERCHANDISING:
NEW PRODUCTS:
PRICING/PROMOTION:
UPLOAD PICTURE:
';
echo $o;
echo"";

echo"
";
    $serverName = "kwe-PC\SQLEXPRESS";
    $connectionInfo = array("Database" => "customerdb", "UID" => "dbadmin", "PWD" => "kwe");

    $conn = sqlsrv_connect($serverName, $connectionInfo);
    if ($conn === false) {
        die(print_r(sqlsrv_errors(), true));
    }
    if (isset($_POST['submit'])) {
	$sql = "UPDATE Customer_Details SET Cust_ID = ".$_POST['cust_id']." WHERE Rec_No =" . $_POST['id'];
    sqlsrv_query($conn, $sql);
	$ids = $_POST['id'];
    
}

	else{
        echo "ID is empty";
    }
?>