Apple Store" app says "momentarily unavailable

It is probably easier to use the App Store function in the Watch app on your iPhone.

Keep trying.

It is probably easier to use the App Store function in the Watch app on your iPhone.

They are not the same. You are thinking of the "App Store" for getting applications.

The iPhone "Watch" app can download apps.

The "Apple Store" on the Apple Watch does things like:

• Show your current Orders.
• Show your Apple Store favorites.
• Show you were the nearest Apple Store is located.
• Show you what training sessions are happening in Apple Stores near you.

The "Apple Store" app on your iPhone can do more, including on-line Apple Store shopping, and searching for products, a Discovery mode (for Apple to market their goods to you). The Apple Watch "Apple Store" is just a subset.