Testing a new AKS Marketplace Product, where do I get an extensionResourceName from?

I've gone through all the steps to create a new containerized product, and am listing it as an AKS Extensions in the Azure Marketplace. I followed this guide: https://learn.microsoft.com/en-us/partner-center/marketplace-offers/azure-container-technical-assets-kubernetes?tabs=windows%2Clinux2

I added an alternate account as a "preview" audience, and everything seems to be working, except anytime I try to put in an "extensionResourceName" the deployment fails, and shows an error about how that name is unavailable. 

From my reading, I seems that my container product will be issued an extensionResourceName when it's published, but I haven't published yet... it's in preview mode for selected members only. 

Where and how can I find an appropriate extensionServiceName to test with?