Client error response [status code] 422

I get this error when creating a client:

Fatal error: Uncaught GuzzleHttp\Exception\ClientException: Client error: 'POST https://api.xsolla.com/merchant/v2/merchants/xxxxxx/token' resulted in a '422 Unprocessable Entity' response: { "http_status_code": 422, "message": "JSON is not valid against json schema, please check documentation https:\ (truncated...) in E:\xamppp\htdocs\vendor\guzzlehttp\guzzle\src\Exception\RequestException.php:113 Stack trace: #0 E:\xamppp\htdocs\vendor\guzzlehttp\guzzle\src\Middleware.php(65): GuzzleHttp\Exception\RequestException::create(Object(GuzzleHttp\Psr7\Request), Object(GuzzleHttp\Psr7\Response)) #1 E:\xamppp\htdocs\vendor\guzzlehttp\promises\src\Promise.php(203): GuzzleHttp\Middleware::GuzzleHttp\{closure}(Object(GuzzleHttp\Psr7\Response)) #2 E:\xamppp\htdocs\vendor\guzzlehttp\promises\src\Promise.php(156): GuzzleHttp\Promise\Promise::callHandler(1, Object(GuzzleHttp\Psr7\Response), Array) #3 E:\xamppp\htdocs\vendor\guzzlehttp\promises\src\TaskQueue.php(47): GuzzleHttp\Promise\Promise::GuzzleHttp\Promise\{closure}() #4 in E:\xamppp\htdocs\vendor\xsolla\xsolla-sdk-php\src\Exception\API\XsollaAPIException.php on line 46

How to fix?

xsolla / xsolla-sdk-php

Client error response [status code] 422 #79