repo initialized with test cases

doc/client.md

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+
+# Client Class Documentation
+
+The following parameters are configurable for the API Client:
+
+| Parameter | Type | Description |
+|  --- | --- | --- |
+| `environment` | `Environment` | The API environment. <br> **Default: `Environment.SANDBOX`** |
+| `timeout` | `int` | Timeout for API calls in seconds.<br>*Default*: `0` |
+| `enableRetries` | `bool` | Whether to enable retries and backoff feature.<br>*Default*: `false` |
+| `numberOfRetries` | `int` | The number of retries to make.<br>*Default*: `0` |
+| `retryInterval` | `float` | The retry time interval between the endpoint calls.<br>*Default*: `1` |
+| `backOffFactor` | `float` | Exponential backoff factor to increase interval between retries.<br>*Default*: `2` |
+| `maximumRetryWaitTime` | `int` | The maximum wait time in seconds for overall retrying requests.<br>*Default*: `0` |
+| `retryOnTimeout` | `bool` | Whether to retry on request timeout.<br>*Default*: `true` |
+| `httpStatusCodesToRetry` | `array` | Http status codes to retry against.<br>*Default*: `408, 413, 429, 500, 502, 503, 504, 521, 522, 524` |
+| `httpMethodsToRetry` | `array` | Http methods to retry against.<br>*Default*: `'GET', 'PUT'` |
+| `loggingConfiguration` | [`LoggingConfigurationBuilder`](logging-configuration-builder.md) | Represents the logging configurations for API calls |
+| `clientCredentialsAuth` | [`ClientCredentialsAuth`](auth/oauth-2-client-credentials-grant.md) | The Credentials Setter for OAuth 2 Client Credentials Grant |
+
+The API client can be initialized as follows:
+
+```php
+$client = PayPalRESTAPIsClientBuilder::init()
+    ->clientCredentialsAuthCredentials(
+        ClientCredentialsAuthCredentialsBuilder::init(
+            'OAuthClientId',
+            'OAuthClientSecret'
+        )
+    )
+    ->environment('Sandbox')
+    ->loggingConfiguration(
+        LoggingConfigurationBuilder::init()
+            ->level(LogLevel::INFO)
+            ->requestConfiguration(RequestLoggingConfigurationBuilder::init()->body(true))
+            ->responseConfiguration(ResponseLoggingConfigurationBuilder::init()->headers(true))
+    )
+    ->build();
+```
+
+API calls return an `ApiResponse` object that includes the following fields:
+
+| Field | Description |
+|  --- | --- |
+| `getStatusCode` | Status code of the HTTP response |
+| `getHeaders` | Headers of the HTTP response as a Hash |
+| `getResult` | The deserialized body of the HTTP response as a String |
+
+## PayPal REST APIs Client
+
+The gateway for the SDK. This class acts as a factory for the Controllers and also holds the configuration of the SDK.
+
+## Controllers
+
+| Name | Description |
+|  --- | --- |
+| getOrdersController() | Gets OrdersController |
+| getPaymentsController() | Gets PaymentsController |
+| getVaultController() | Gets VaultController |
+| getOAuthAuthorizationController() | Gets OAuthAuthorizationController |
+