How do I get a proof of purchase for my iPhone 16?

You have posted not to Apple, but to literally thousands of users on this user to user only forum, which Apple doesn't participate. And you posted your email address and phone number, which is most unwise. I have asked the moderators to edit out your personal information for your protection.

We cannot send you your receipt. We don't know you or have access to anything about your or what you have purchased.

When you buy an iPhone from Apple they send you a copy of your receipt via email. Didn't you store a copy of it for future reference? If no, assuming you actually bought the phone from Apple, on your iPhone open the Apple Store (not App Store, but Apple Store) app. Tap your initial in the circle at the top right hand corner, then tap Orders and look for your iPhone purchase. Tap it and print the receipt there.

User to user support forum.

No one here is going to email you anything.

You need to contact whatever retailer you purchased your device from and get a receipt from them.

Don’t post personal information on the internet.

"How do I get a proof of purchase for my iPhone 16?: I purchased an iPhone 16 and need a proof of purchase please send me a proof of purchase my email is [...]and phone number is [...]"

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Get an Invoice:

So, see if you can get an invoice to provide a proof of purchase.

1. Go Here: Viewing & Changing Orders - Apple Support
2. Scroll to: View or Print Invoice (very bottom)
3. Proceed from there as necessary