TIdHTTP REST OAuth2

[Boba TC]

Dear Reader;
in my 1st attempt to connect to a REST server with TIdHTTP all I was told to do is to POST an HTTP request in the form:
"https://www.server.com/api/authentication/oauth2/token?grant_type=password&username=***&password=***&client_id=***&client_secret=***"
with server-side generated username, password, client_id and client_secret:

Code:

TIdHTTP *IdHTTP;
TIdSSLIOHandlerSocketOpenSSL *IdSSLIOHandlerSocketOpenSSL1;
TIdLogFile *IdLogFile1;
AnsiString sURL0, sResp;
IdHTTP->IOHandler = IdSSLIOHandlerSocketOpenSSL1;
IdHTTP->Intercept = IdLogFile1;
TStringList *slHttpRspns;
//...
  sURL0 = "https://www.someserver.com/api/authentication/oauth2/token?grant_type=password&username=nome_de_usuário%40oldshoes.com&password=metellno1&client_id=wqeqweqwewqwewq&client_secret=qwewqewewqe";
  try{
    slHttpRspns = new TStringList;
    IdLogFile1->Active = true;
    sResp = IdHTTP->Post( sURL0, slHttpRspns );
    Memo1->Lines->Add( "IdHTTP->ResponseCode="+IntToStr(IdHTTP->ResponseCode) );//500
    //if succeeded the server should come back with a token in JSON form
  }catch( Exception &e ){
    //...
  }

IdHTTP->ResponseCode==500;

IdLogFile has the following:

Stat Connected.
Sent DateTime: POST /api/authentication/oauth2/token?grant_type=password&username=nome_de_usuário%40someclient.com&password=metellno1&client_id=wqeqweqweqewqwewq&client_secret=qwewqewqewqewqe HTTP/1.1
Content-Type: application/json
Content-Length: 0
Host: www.someserver.com
Accept: text/html,application/xhtml+xml,application/xml,application/json;q=0.9,*/*;q=0.8
User-Agent: Mozilla/3.0 (compatible; Indy Library)

Recv DateTime: HTTP/1.1 500 Server Error
Content-Length: 347
Content-Type: application/json
Strict-Transport-Security: max-age=31536000; includeSubDomains;
Content-Security-Policy: default-src 'self'; font-src *;img-src * data:; script-src *; style-src *;
Referrer-Policy: strict-origin
X-Content-Type-Options: nosniff
X-Frame-Options: SAMEORIGIN
X-SL-Proxy: false
X-XSS-Protection: 1; mode=block
Date: DateTime

{
  "failure" : "Pipeline execution failed while waiting for output",
  "reason" : "Snap errors: {ruuid=<***some guid***>, label=Decode JSON, failure=Failed to read from binary input view, reason=No content to map due to end-of-input, resolution=Please address the reported issue.}",
  "resolution" : "Fix the reported errors"
}

JSON at the bottom of IdLogFile is the server Error detailed.

I have no idea what all that is about, so I ran that same request with PostMan ver.9.31 - it came back with no error and new token in its response.

What do I need to change on VCL/Indy side in order to mimic the PostMan's behaviour? Is this information enough to correct the error?

Please help. Thanks in advance. Boba TC.