I think there is likely some further configuration that is missing / not yet in place. See my response to your related question on your original thread:
Hi @dasra23 ,
I’m glad that was useful. I am, unfortunately, not familiar with the Azure Dev Centers as I have never used them so I am unlikely to be able to help with specifics related to their configuration.
However, this error seems to require an ‘attached network’ and, looking at the AZAPI documentation it should be available as a data resource if it is attached: Microsoft.DevCenter/projects/attachednetworks . If it is not (which the error seems to suggest) then you are likely to be missing…