Route forwarding in V3

I have Googled and found a few suggestions but they seem to be for v2 as the API is different.

Anywho I have a route “/register” which handles both the get and post methods. The GET generates the form and the POST should process the submission request - however upon failure I would like to forward to the GET handler to re-populate the form with submitted values. As opposed toi storing the values in a SESSION and redirecting.

In full stack frameworks this is usually simple but for the life of me I cannot find any documentation on how this might be accomplished in Slim v3 - can you demonstrate?

you need to save the data to a session and pull it into your view.