容易理解，您可以使用array_chunk()，array_sum()，array_column()如下：-

$new_array = array_chunk($array,10);
$sub_total_array = [];
foreach($new_array as $array){
   $sub_total_array[] = array_sum(array_column($array,'amount_paid'));
}
print_r($sub_total_array);

包含range、array_slice和array_column函数的简短解决方案：

// $arr is your initial array
$sub_totals = [];
foreach(range(0, count($arr), 10) as $k){
    $sub_totals[] = array_sum(array_column(array_slice($arr, $k, 10), 'amount_paid'));
}

• range(0, count($arr), 10)-生成一个包含一系列元素的数组。它将是[0, 10, 20]。这些元素是每个大小为10的序列的边界
• 每个下一边界$k用于从初始阵列$arr中提取下一个10大小的序列/片段

$ret = array();
$subtotalamount = 0;
for ($i = 0; $i < count($json); $i++) {
    $subtotalamount += floatval($json[$i]['amount_paid']);
    if ($i % 10 == 9) {
        $ret[] = $subtotalamount;
        $subtotalamount = 0;
    }
}
if ($subtotalamount > 0) {
    $ret[] = $subtotalamount;
}

试试这个，

$sumofall = array();
for ($i = 0; $i < count($json); $i++) {
    if ($i % 10 == 0) {       
        $sumofeach = 0 
        for ($j=$i-10;$j<$i-1;$j++) {
            $sumofeach += floatval($json[$i]['amount_paid']);
        $sumofall[] = $sumofeach
    }
}

$a = array (0 => array ( 'amount_paid' => 2050.00 ), 1 => array ( 'amount_paid' => 2050.00 ) , 2 => array ( 'amount_paid' => 2050.00 ) , 3 => array ( 'amount_paid' => 2050.00 ) , 4 => array ( 'amount_paid' => 2050.00 ) , 5 => array ( 'amount_paid' => 2050.00 ) , 6 => array ( 'amount_paid' => 2050.00 ) , 7 => array ( 'amount_paid' => 2050.00 ) , 8 => array ( 'amount_paid' => 2050.00 ) , 9 => array ( 'amount_paid' => 2050.00 ) , 10 => array ( 'amount_paid' => 2050.00 ) , 11 => array ( 'amount_paid' => 2050.00 ) , 12 => array ( 'amount_paid' => 2050.00 ) , 13 => array ( 'amount_paid' => 2050.00 ) ) ; 

$b = array_column($a,'amount_paid');

$c = array_chunk($b,10);

$sum = [];
foreach($c as $arr){
    $sum[] = array_sum($arr);
}

echo "sum = ";
print_r($sum);

与@Anant的答案相同的函数风格是使用array_map()。
代码：（Demo）

var_export(
    array_map(
        fn($set) => array_sum(array_column($set, 'amount_paid')),
        array_chunk($array, 10)
    )
);

在经典循环中，访问列值，并在将第一级索引除以10时使用截断被除数将求和值推入其各自的组中。
代码：（Demo）

$result = [];
foreach ($array as $i => $row) {
    $group = intdiv($i, 10);
    $result[$group] = ($result[$group] ?? 0) + $row['amount_paid'];
}
var_export($result);