From the Garmin product page for Vívoactive 3:

vívoactive 3 is our first wearable to feature Garmin Pay, which lets you pay for purchases with your watch. Use it just about anywhere you can tap your card to pay1. So, if you left your wallet in your locker or just forgot it, that post-run morning caffè latte can still be yours. Just tap and go.

Sounds like Garmin has been losing sales due to the Apple Watch and decided it needs to compete with similar features.