My iPad Air 2 wont sync with my iPhone without Wi-Fi

Depends on what you mean by "syncing".

In the normal sense of transferring information back and forth, they don't really sync.

Continuity features may allow the iPad to place calls when the iPhone is nearby.

Message Forwarding does not require the iPhone be near by or on the same Wi-fi network however.

Other Continuity features require the iPad and iPhone to be on the same Wi-fi network.

Things like Contacts, notes, calendar, email iCloud Drive files, iCloud photos and iCloud music can sync between the devices over the internet and don't require the devices to be close to each other.

What exactly is not syncing?

Please be specific about what is not happening that you think should.

iPhones and iPads interact in different ways, and the options they have have different requirements.

click here ➜ Continuity features and requirements for Apple devices - Apple Support

Tydiis wrote:

Thanks! Is there documentation that proves this?

The link Phil0124 explains how continuity works. Here's another one which may help you --> Use Continuity to work across Apple devices - Apple Support

An iPhone and iPad don't sync with each other at all, no matter what network they are on.

They sync with iCloud and whatever other cloud service you use. If something isn't syncing, it's because a device isn't communicating with iCloud or another cloud service.

Tydiis wrote:

Thanks! Is there documentation that proves this?

Proves what?

You haven't explained what is not syncing.

iCloud data sync, is done through iCloud and does not require device being near each other.

For other features, check the continuity link I provided for their requirements.

here it is again, click here ➜ Continuity features and requirements for Apple devices - Apple Support

Tydiis wrote:

Thanks! Is there documentation that proves this?

Sorry? To prove what?

How about you show us the documentation showing that it is possible to directly sync an iPhone and iPad with each other...