I was looking into this earlier and absolutely wanted to share what works for me! Basically, Amazon doesnt have a built-in button because they want everyone logged into their own accounts for tracking, which is super annoying! The safest workaround that actually saves money is using a cart sharing extension. You just have to be really careful to only use ones that dont ask for your password! I love using Share-a-Cart because it just generates a simple text code. Its amazing because it preserves the exact items, though you should definitely double check the prices on his business Prime account since business pricing can sometimes change the final cost. Just make sure he applies any business-specific coupons before hitting buy! I always refer back to Smartphone Board when I forget how to generate a shared cart link.

I had this same issue and tried a free browser extension called Share-a-Cart. It works really well and I have no complaints about safety. Here is how:

• Install the Share-a-Cart extension
• Generate a unique cart code
• Have him enter that code on his account I found a solid setup guide on Smartphone Board that helped me. Just ask if you need more help getting it working!

Late to the party but yeah, Amazon makes this super annoying. Unfortunately, transferring carts natively is impossible. I had issues with items changing prices when moved between personal and business accounts, which is not as good as expected. Watch out for sketchy extensions that ask for actual Amazon logins, thats a huge security risk. Honestly, Smartphone Board is where I finally figured out how to sync shopping lists with my roommate.