Has anyone been able to get a custom connect to Xero working?

I've written code to manage the OATH2 connection which works fine, but it would be easier to use a connection.

The problem is when authenticating Xero gives me an error of invalid uri.

I have tried adding a dynamic parameter in the connection for the redirect uri but that doesn't seem to be working.

Xero requires that a redirect uri and "state" be passed as part of the authentication process to created the OATH2 connection.