php implode multidimensional array
$users = [
	'users' => ['[email protected]','[email protected]'],
	'admins' => ['[email protected]', '[email protected]']
];
// function to convert array of arrays to string
function implodeArrayofArrays($array, $glue  = ', ') {
        $output = '';
        foreach ($array as $subarray) {
            $output .= implode($separator, $subarray);
        }
        return $output;
}
echo implodeArrayofArrays($users);
// "[email protected], [email protected], [email protected], [email protected]"