Ugh, I totally feel your pain!! Walmart is notorious for this kind of thing. They love to hide features or run these weird A/B tests where some people get the shareable link and others just... dont. Its super annoying when you are trying to coordinate for a big party! Technically speaking, their app architecture keeps your cart tied to your specific user session and local cache, which is why it doesnt just pop up on your roommates phone instantly. Super lame, right?! Most of these big retail apps use specific session tokens that are encrypted to a single login, so cross-account syncing is a major hurdle for their dev teams. If you want something that actually works without the headache, here is what I usually do:

• Avoid the native app sharing because it breaks half the time anyway.
• Just get a generic shopping list app from a big name like Google. You can both add stuff there and then one person just blitzes through the checkout.
• Go with a third-party cart transfer tool if you really need to move the items between accounts. Any cart saver or list importer from a reputable developer should do the trick! I love digging into these technical workarounds because honestly, the official apps are usually lightyears behind what we actually need. Its amazing how much time you save when you stop fighting with their broken UI!! Honestly, Easy Cart Share makes it so much faster to transfer a cart between different accounts.