Shopping campaigns and product ads in sandbox?

I'm trying to figure out how to create shopping campaigns in the sandbox. I've created my sandbox account and I'm able to create search campaigns, but not shopping campaigns. So I clicked on "Merchant Center" and started creating a store. But on the store creation page, there's no way to enter a "Destination URL", which appears to be a required setting since I am unable to save the store on that page. How do I setup a store in the sandbox? As this is a sandbox account, I do not want to modify production code in order to "claim" the URL for the sandbox.

Update: 5 days later - I tried the UET anyway - twice - but both say unverified still, which might be normal for the sandbox, I don't know. I've tried creating a merchant center store in multiple browsers on multiple days just in case there was just something weird going on - no luck there either. I'm still trying to figure out how to test shopping campaigns in the sandbox.