curl -X PUT https://api2.ecomailapp.cz/lists/1/update-subscribers-bulk \
  -H "key: YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "subscriber_data": [
      {
        "email": "foo@bar.cz",
        "name": "Jan",
        "surname": "Novak",
        "custom_fields": { "shop": "myshop.cz" },
        "tags": ["vip"]
      },
      {
        "email": "foo2@bar.cz",
        "name": "Jana"
      }
    ],
    "allow_resubscribe": false
  }'

$listId = 1;
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, "https://api2.ecomailapp.cz/lists/{$listId}/update-subscribers-bulk");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_CUSTOMREQUEST, 'PUT');
curl_setopt($ch, CURLOPT_HTTPHEADER, [
    'key: YOUR_API_KEY',
    'Content-Type: application/json',
]);
curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode([
    'subscriber_data' => [
        [
            'email' => 'foo@bar.cz',
            'name' => 'Jan',
            'surname' => 'Novak',
            'custom_fields' => ['shop' => 'myshop.cz'],
            'tags' => ['vip'],
        ],
        [
            'email' => 'foo2@bar.cz',
            'name' => 'Jana',
        ],
    ],
    'allow_resubscribe' => false,
]));
$response = curl_exec($ch);
curl_close($ch);

{
  "updates": 2
}

{
  "errors": {
    "subscriber_data.0.email": ["Invalid email address"],
    "subscriber_data.0.custom_fields": [
      "Custom fields must be an array with unique keys (case-insensitive)",
      "Subscriber custom fields must be an array with max 5000 bytes"
    ]
  }
}