OAuth with PKCE

[phoinv]

I am trying to implement the code grant flow with PKCE. The client ID I have is configured to use PKCE.

The URL accessed:

https://connect.visma.com/connect/authorize?response_type=code&client_id=isv_xxxx&redirect_uri=https...

The URL return contains the code:

https://redirecturi/?code=xxxxxxxx&scope=profile%20email%20openid%20vismanet_erp_interactive_api%3Au...

When exchanging the code for an access token returns a HTTP 400 with the body:

```

{"error":"invalid_grant"}

```

The request contains the `grant_type=authorization_code`, including the `code`, `client_id`, redirect_uri` and `code_verifier` as per the specification (https://docs.connect.visma.com/docs/native-applications).

There is no error code returned, so no way to see more information on the reason of the error.

What can be the cause of this issue?