Laravel 5.4 Passport: unsupported_grant_type

You need to install a password client for Passport. Assuming you've installed and configured Passport, to generate a password client, run:

php artisan passport:client --password

Make sure to use the details from the output of this command in your API requests.

inside form-data in postman use following

grant_type : password

client_id  :  2

client_secret : vSFxVqALQHjyotPyGfhrGj3ziudUGsts2ZWiAGms or whatever this is 

username: [email protected] 

password: mypassword

scope: 

You can get client id and secret from oauth_clients table if no data there use following command to create a client

php artisan passport:client --password

use the oauth_clients table particular row, where password client column value is 1
see how i have integrated token generation code with login. I used right format to solve grant issue in laravel 5.8

public function login(Request $request) {
    if (Auth::attempt(['email' => request('email'), 'password' => request('password')])) {
        $user = Auth::user();

         if(Auth::check()) {  // check whether user exist
           $req = Request::create('/oauth/token', 'POST',[
                     'grant_type' => 'password',
                     'client_id' => 2,
                     'client_secret' => 'WDv6wrY9Tf9HuixaiQjDWGy7yBqEG1IrmsLucAUI',
                     'username' => request('email'),
                     'password' => request('password'),
                     'scope' => '' 
                   ]);   
                   $res = app()->handle($req);
                   $responseBody = json_decode($res->getContent()); // convert to json object
           return response()->json(['success' => $responseBody], $res->getStatusCode());

         } else {
            return response()->json(['error' => 'Not logged in '], 401);
          }

    } else {
        return response()->json(['error' => 'Authentication failed '], 401);
    }
}