Oppo Watch Faq page 40

Google Pay is currently only available in certain countries and
regions. To use Google Pay, you need to be in Australia, Canada,
France, Germany, Switzerland, Italy, Poland, Russia, Spain, UK, or
US.
6.2.2 How to add a card？
1. On your watch, open the Google Pay app.
2. Tap "Get started".
3. Set up "Screen lock" (if you haven't already).
4. On your phone, follow the instructions to add a credit or debit
card. Note: This only adds a card to the Google Pay app on
your watch (not your phone).
6.2.3 How to Make a payment in a store?
1. On your watch, open the Google Pay app.
2. Hold your watch over the contactless payment reader until
you hear a sound or feel vibration from your watch.
3. If asked, choose "Credit" regardless of your type of card.
4. For debit card transactions, you may have to enter a PIN. Use
the PIN you set up with your bank.
6.2.4 How to delete a card？