Hi,
Sorry, but had few questions to clarify:
1. As I understand your core interfaces are on rlt- right? What IGP protocol you are running here? Do you have the corresponding IGP session up? If you are using ISIS as the IGP, you need to enable family iso as well.
2. Do you see IPV6 neighbourship up on rlt-?
3. The documentation link which you shared initially also talks about enabling "deaggregate" and "transport-preference", have you played it with that and see if that helps?
4. Here is the example of a working configuration:
Thanks