Authorization returns 400 bad request from trying with front end.

[VipinVijay]

I am trying the oauth flow for developing an app for shopify from the instructions given in the link below:
https://help.shopify.com/en/api/getting-started/authentication/oauth

So, in the step 3 when I try to make a 'POST' request to retrieve the access token I am sending all the given parameters i.e(client_id,client_secret) in the request body in json format. But then I am receiving 400 Bad Request. In response it also shows "Oauth error invalid_request: The authorization code was not found or was already used".

Can you please help me with this?

Can you check my x-request-id-8aae18b9-ee4f-49ee-98b0-18272b73c044