You will need to replace the {client id} in the redirect URL with the ClientId of your OAuth2 client. For example in the screenshot below I have a client with id "_nEqqrlx7tQQL2y)PUAKaaMzKmkJGTCkQ1h-on7". To enable redirecting on that client I have set my Authorized Redirect URI to: "https://lucid.app/oauth2/clients/_nEqqrlx7tQQL2y)PUAKaaMzKmkJGTCkQ1h-on7/redirect.

Information about configuring your OAuth2 client can be found here.  Once your OAuth2 client is configured you will no longer get the "page not found" error when authenticating.