Where do I find he Dashlane UKI? Dashlane support doesn't know what this is.
Firstly, you need a Dashlane premium subscription.
Secondly, to get the Dashlane UKI, you simply need to press the Get New UKI button. This should send you a new code via email and then, you can copy/paste it inside RDM.
In conclusion, you should now be able to fetch your credentials from Dashlane into RDM.