The “Create Extension” menu item is disabled. How can I enable it?

I’m aware of the fact that the model that owns the table i’m trying to extend must be referenced.
However, after following Dynamics 365 > Model Management > Update Model Parameters. The model that owns the table I’m trying to end isn’t available for selection.
What could have gone wrong?
The fact that extensions can’t be created in your current projects (but you could do it in a new project) indeed means that your project is for a model that doesn’t have a reference to the model you want to extend.
Please tell us more about your actual problem, i.e. they you can’t add the reference. The picture above doesn’t show anything that could help us to spot the problem. Also, you didn’t tell us whether it worked before nor how you installed the model.
Thanks Martin. The project that houses the table I’m trying to extend from is not currently referenced. The name of the project is DPR_HSE_Safety

DPR_HSE_Safety is missing from the available packages…
The main challenge is how do I add the project?
In other words, the project that contains the table I’m trying to extend is not referenced at the moment. How can I reference it?
How did you install the model? Are you sure about the name? Did you verify that you a descriptor file for this model?