How to convert "rate" at simple queue using mikrotik API in PHP

RouterOS Scripting
1

Hello, I’m connecting to the Mikrotik API in PHP, and when I get the rates they are in bytes format, so how do I convert them to MB or GB and so on..
I use the format bytes ($bytes / 1000) it can’t be done because the rate has pair values, so how to change it?

<td><?php echo formatBytes($rate,2);?> </td>

here is code fo format bytes :

function formatBytes($bytes, $decimal = null)
 {
	$satuan = [' Bytes', ' KB', ' MB', ' GB', ' TB'];
	$i = 0;
	while ($bytes > 1024){
	$bytes /= 1024;
	$i++;
	}
	return round($bytes, $decimal). '' . $satuan[$i];
}

The eror says : Notice: A non well formed numeric value encountered