Login from app-flutter

Hello,
I am using the app-flutter android app and I have problem with the login.
By debuging the app with android studio I found the call it makes to the server and reproduce it through restman for firefox as below.

POST
https://xxxxxxxxx/apis/api/auth
data:
{“grant_type”:“password”,“username”:“Secretary”,“password”:"!Secretary2021!",“scope”:“default”}

And i get the server response
“400 Bad Request”

I am using openemr 6 patch 3.
What is the correct form of api login ?

Any help is appreciated.