Magento 2 – How to Create or Update Customer Information Using REST API

I found the solution on this link. and here is the explanation on it.

You can define the limit of items returned in the response by passing the limit parameter. By default, 10 items are returned and the maximum number is 100 items. You can also define the page number by passing the page parameter. Example:

http://magentohost/api/rest/products?page=2&limit=20

Create New Customer

    $userData = array("username" => "admin", "password" => "admin123");
    $ch = curl_init("http://magento213/index.php/rest/V1/integration/admin/token");
    curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "POST");
    curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($userData));
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($ch, CURLOPT_HTTPHEADER, array("Content-Type: application/json", "Content-Lenght: " . strlen(json_encode($userData))));

    $token = curl_exec($ch);


    $customerData = [
        'customer' => [
            "email" => "user@example.com",
            "firstname" => "John",
            "lastname" => "Doe",
            "storeId" => 1,
            "websiteId" => 1
        ],
        "password" => "Demo1234"
    ];

    $ch = curl_init("http://magento213/index.php/rest/V1/customers");
    curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "POST");
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($customerData));
    curl_setopt($ch, CURLOPT_HTTPHEADER, array("Content-Type: application/json", "Authorization: Bearer " . json_decode($token)));

    $result = curl_exec($ch);

    $result = json_decode($result, 1);
    echo '<pre>';print_r($result);

For Update Customer

$customerData = [
    'customer' => [
        'id' => 10,
        "email" => "user@example.com",
        "firstname" => "John2",
        "lastname" => "Doe2",
        "storeId" => 1,
        "websiteId" => 1
    ],
    "password" => "Demo1234"
];

$ch = curl_init("http://magento213/index.php/rest/V1/customers/10");
curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "PUT");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($customerData));
curl_setopt($ch, CURLOPT_HTTPHEADER, array("Content-Type: application/json", "Authorization: Bearer " . json_decode($token)));

$result = curl_exec($ch);

$result = json_decode($result, 1);
echo '<pre>';print_r($result);

API LIST Create a customer account