Can't exchange authorization code to access token in eBay

I am following a documentation for eBay API and I have done previous steps by enabling OAuth in eBay app for developer. I have got authorization but I can't exchange it for access token. It keep showing me following error:

{
    "error": "server_error",
    "error_description": "server encountered an unexpected condition that prevented it from fulfilling the request"
}

I have tried running this in my PHP Laravel Controller and in Postman. Getting same error:

$curl = curl_init();

curl_setopt_array($curl, array(
  CURLOPT_URL => 'https://api.sandbox.ebay.com/identity/v1/oauth2/token',
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => '',
  CURLOPT_MAXREDIRS => 10,
  CURLOPT_TIMEOUT => 0,
  CURLOPT_FOLLOWLOCATION => true,
  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
  CURLOPT_CUSTOMREQUEST => 'POST',
  CURLOPT_POSTFIELDS =>'grant_type=authorization_code&code=v%5E1.1%23i%5E1%23p%5E3%23f%5E0%23I%5E3%23r%5E1%23t%5EUl41XzM6RURBMkI0QkQ3RDZGNzVBNzY3RTRFQjUwODk3REE3QzVfMF8xI0VeMTI4NA%3D%3D&redirect_uri=Muhammad_Tayyab-Muhammad-OTIFTE-epcga',
  CURLOPT_HTTPHEADER => array(
    'Content-Type: application/x-www-form-urlencoded',
    'Authorization: Basic TXVoYW1tYWQtT1RJRlRFU1QtU0JYLWNhYzMyODgwMi02ODMwYjc1YzpTQlgtYWMzMjg4MDI1Yjk1LTdjOGQtNDgyMC1iMjQ1LTlmNWQ=',
    'Cookie: dp1=bu1p/QEBfX0BAX19AQA**69fc443e^; ebay=%5Esbf%3D%23%5E'
  ),
));

$response = curl_exec($curl);

curl_close($curl);

Link to the doc:

https://developer.ebay.com/api-docs/static/oauth-auth-code-grant-request.html

I don't know what I am doing wrong here. I can't find official postman collection for ebay API.

Solution

Your curl request is fine. It seems your <client_id> is incorrect. When I decoded your base64 encoded OAuth credentials, I got this:

"   uhammad-OTIFTEST-SBX-cac328802-6830b75c:SBX-ac3288025b95-7c8d-4820-b245-9f5d"

You can check it out here.

I replaced the "tab" with "M" and retried then, I got this new error:

{
    "error":"invalid_grant",
    "error_description":"the provided authorization grant code is invalid or was issued to another client"
}

It can be considered as a good progress! I hope it helps you to fix the problem.