My Apple Watch Series 3 won’t sync with my iPad Air third generation

Use the same Apple ID on all your participating devices.

Update Watch to watchOS 7.2, iPhone to iOS 14.3, and iPad to iPadOS 14.3

Also see my post above.

Note: You do not pair an Watch with an iPad.

No, the Watch is not paired to an iPad like you do with an iPhone.

It connects using Bluetooth.

Start a workout => Work out with Apple Fitness+ - Apple Support

Is Watch updated to watchOS 7.2?

Is iPad updated to iPadOS 14.3?

FYI: First, you have to update the devices.

Have your Apple ID and password ready. And make sure that two-factor authentication is set up for your Apple ID.

How to subscribe to Apple Fitness+ on your iPad

1. Download the Fitness app from the App Store.
2. Open the Fitness app.
3. Tap Get Started.
4. Tap the trial offer (one trial per person or family).
5. Sign in with your Apple ID and password. Forgot your Apple ID?
6. Verify your billing information and add a valid payment method.
7. Tap Subscribe.

1. Are both devices (Watch and iPad) using the same Apple ID & password?
2. And make sure that two-factor authentication is set up for your Apple ID.
3. Check both devices Settings > Bluetooth > ON
4. See my previous post instructions on downloading Fitness app and starting the workout.

Also check your paired iPhone.

An Apple watch requires an iphone to pair,setup and function,not an ipad.