Unable to request new access token but manually set access token works

[arshohag]

I am trying to integrate in laravel 6 & Guzzle 6.3. But facing the problem. Although manually set OAuth access token works fine.
Here's my request parameter for obtaining access token -
"grant_type" => "password",
"client_id" => "api-client",
"username" => $username,
"password" => $password,
"broker" => $broker,

I put this in config but seems it always shows the error. Any suggestions?