รบกวนด้วยครับติด Warning: implode(): Invalid arguments passed

<?php
$con = mysqli_connect("localhost", "root", "", "ecommshoes");

	$get_pro_style = "select * from  product where product_cat = 1 LIMIT 0,6 ";
	
	$run_pro_style = mysqli_query($con, $get_pro_style);
	
	while($row_pro_style = mysqli_fetch_array($run_pro_style)){
?>
<form action="test_product1_test.php" method="post" name="form1">
<label>
		<input type='radio' name='shoes_style' value='<?php echo $row_pro_style["product_id"];?>'>
		<?php echo $row_pro_style["product_id"];?><br />
		
		<?php echo $row_pro_style["product_title"];?><br />
		
		<img src='admin_area/product_image/<?php echo $row_pro_style["product_image"];?>' /><br />
		------------------------------------------------<br />
</label>		
<?php		
	}
?>
<input type="submit" value="Provide Fit" name="submit" id="submit" class="button-button" />
</form>

<?php
error_reporting(E_ALL & ~E_NOTICE);
$con = mysqli_connect("localhost", "root", "", "ecommshoes");
	$in_value = implode("," , $_POST["shoes_style"]);
	$sql = mysqli_query($con, "select * from  product where product_cat in ('$in_value')");
?>
<?php
while( $r = mysqli_fetch_assoc($sql)){
	?>
	<?php echo $r["product_id"];?><br />
		
		<?php echo $r["product_title"];?><br />
		
		<?php echo $r["product_price"];?><br />
		
		<img src='admin_area/product_image/<?php echo $r["product_image"];?>' /><br />
	
	
<?php	
}
?>