Face ID is not working on iPhone 16 Pro Max

Hello!

Try these steps: If Face ID isn't working on your iPhone or iPad Pro - Apple Support

If no success, continue bugging the store for a replacement. They shouldn’t sell you an iPhone that doesn’t work. Also 10 days is within the 14 day refund period you’re entitled to if you’re not happy with your purchase.

Is this store an official Apple Store or Authorized Apple Reseller?

If this was Apple or an Apple Authorized Reseller, they couldn’t have denied your refund. They offer a 14 day refund and exchange period which you are still in. Now the only time this policy wouldn’t apply is if this was an Unauthorized Reseller, which from my look at Apples list of Authorized Resellers, I couldn’t find the store you purchased it from. As a result we don’t know what happened to the iPhone before you, it may have been used or incorrectly refurbished, but you are subject to their return policy, if they even have one which doesn’t seem so. And even if you were out of Apple’s return period, they likely would have offered you a free repair within the 1 Year Limited Manufacturers Warranty. Unfortunately there’s nothing Apple can do now and you’ll have to work this out with the store. Next time only purchase from Apple or Authorized Resellers.

After only 10 days?

Stop right there, you purchased a defective product.

🛑 Return it for a full refund A.S.A.P. ⚠️

Good luck! 👋🏼😉