To reiterate what @AnthonyRyanEQL , that extension is only required once you upgrade to 11.2 or later, which if you're on the Network Management Release plan won't be until you upgrade to 11.3.
The most likely scenario is that there is a typo in the version name you are using. Can you post a screenshot of the version name you're trying to reconcile and the corresponding version name in the version management dialog (or the version name from the rest endpoint)?