Oauth token unauthorized with JWT

Hi, I have enabled Auth0 as IDP with SSO in Salesforce. I am trying to get the access token with JWT in salesforce.
https://dev-vbrsc3ue.us.auth0.com/oauth/token
granty_type: urn:ietf:params:oauth:grant-type:jwt-bearer
assertion: //JWT value

I am receiving the below response.
{
“error”: “access_denied”,
“error_description”: “Unauthorized”
}