"Unexpected code_verifier" when trying to achieve authorization in hybrid flow (with PKCE) using IdentityServer4

Question

I'm trying to implement native clients (.NET Console applications as a mockup at first) to authenticate using OpenID Connect against IdentityServer4 as my STS. I use IdentityModel.OidcClient2 as my client library.
I chose to implement the code based authentication flow.

I am able to pass through the authentication stage but when I get to the authorization stage I get an error message at the client saying

invalid_grant

At the IdentityServer the error message is

"Unexpected code_verifier: XXXXXXXXXXX...."

Even though when I open fiddler and look at the requests and the debug info - the code verifier sent to the IdentityServer for the authorization seems as the client generated at first in the AuthorizationState class.
If I execute with AuthorizationState.CodeVerifier = null then it works.
But I do want to implement the PKCE for extra security. How can I achieve that?

Here is the configuration of that specific client
Identity Server :

            new Client
            {
                ClientId = "nativeapp1",
                ClientName = "Native App Demo - 1",
                AllowedGrantTypes = GrantTypes.Hybrid,

                RequireConsent = true,

                ClientSecrets =
                {
                    new Secret("some-secret1".Sha256())
                },

                AllowedScopes = {
                    IdentityServerConstants.StandardScopes.OpenId,
                    IdentityServerConstants.StandardScopes.Profile,
                    IdentityServerConstants.StandardScopes.OfflineAccess,
                    "custom.name",
                    "api1"
                },

                RedirectUris = {"http://127.0.0.1:7890/"},
                //PostLogoutRedirectUris = {"" }
                AllowOfflineAccess = true
            }

And the client configuration

var options = new OidcClientOptions
        {
            Authority = _authority,
            ClientId = "nativeapp1",
            RedirectUri = redirectUri,
            Scope = "openid profile api1 custom.name offline_access",
            FilterClaims = true,
            LoadProfile = false,
            Flow = OidcClientOptions.AuthenticationFlow.Hybrid,
            ClientSecret = "some-secret1"
        };

Answer 1

You need to set RequirePkce to true on you client configuration in IdentityServer.