Error: "invalid-token-response" - WordPress 5.4.2 oauth2 client / Nextcloud 19 (OAuth2-Provider)

i get an Error: "invalid-token-response" error when using oauth2 WordPress 5.4.2 with OpenID Connect Generic Plugin 3.6.0 Nextcloud 19 (OAuth2-Provider)

what am i doing wrong?

this is the log in the OpenID Connect Generic Plugin:

Typ: make_authentication_url
Datum: 2020-07-16 07:14:57
Benutzer: 0
URI: /wp/wp-login.php?login-error=invalid-token-response&message=Invalid+token+response
Data: string(349) "http://auth0.mydomain.de/nc/index.php/apps/oauth2/authorize?response_type=code&scope=openid%20profile%20email&client_id=ta0XeuISWT9cZB5lojfODJuL4mkXhVijh7rrzgETAquyuAcGQVK4Yg414nuFzcpj&state=604f27813e83e814854391957a830788&redirect_uri=https%3A%2F%2Fauth0.mydomain.de%2Fwp%2Fwp-admin%2Fadmin-ajax.php%3Faction%3Dopenid-connect-authorize"

Typ: invalid-token-response
Datum: 2020-07-16 07:14:57
Benutzer: 0
URI: /wp/wp-admin/admin-ajax.php?action=openid-connect-authorize&state=1efc17338ebeb61f3f1d37da3fe7867c&code=
    Data: object(WP_Error)#7808 (2) {
      ["errors"]=>
      array(1) {
        ["invalid-token-response"]=>
        array(1) {
          [0]=>
          string(22) "Invalid token response"
        }
      }
      ["error_data"]=>
      array(1) {
        ["invalid-token-response"]=>
        array(5) {
          ["access_token"]=>
          string(72) "6WQ23PeixVHPyyhfXQk3ZDVze4UeBxdf9RsXRwU6w9CToLJW1VWPbFboFRQgvRUi9FfxG71D"
          ["token_type"]=>
          string(6) "Bearer"
          ["expires_in"]=>
          int(3600)
          ["refresh_token"]=>
          string(128) "zSRCTRWqZcD5izDpHZTACr4WGW20YrTQtNBivAELocLqD8RJ5bUCnPHnjMPUfzzGJ3g2jCn9xR7EW3Qj2EC8xcC35ekeaEVikrpVRhztMOWptlHjOnYGt9DuuXoYPA9U"
          ["user_id"]=>
          string(6) "theUser"
        }
      }
    }

Typ: request_authentication_token
Datum: 2020-07-16 07:14:57
Benutzer: 0
URI: /wp/wp-admin/admin-ajax.php?action=openid-connect-authorize&state=1efc17338ebeb61f3f1d37da3fe7867c&code=
    Data: string(68) "http://auth0.mydomain.de/nc/index.php/apps/oauth2/api/v1/token"

Typ: make_authentication_url
Datum: 2020-07-16 07:14:50
Benutzer: 0
URI: /wp/wp-login.php?loggedout=true&wp_lang=de_DE
Data: string(349) "http://auth0.mydomain.de/nc/index.php/apps/oauth2/authorize?response_type=code&scope=openid%20profile%20email&client_id=ta0XeuISWT9cZB5lojfODJuL4mkXhVijh7rrzgETAquyuAcGQVK4Yg414nuFzcpj&state=1efc17338ebeb61f3f1d37da3fe7867c&redirect_uri=https%3A%2F%2Fauth0.mydomain.de%2Fwp%2Fwp-admin%2Fadmin-ajax.php%3Faction%3Dopenid-connect-authorize"