The wallet app shows that my area cannot be used, but my area is already in Singapore.

Hello and welcome to Apple Support Communities, hiijingyee!

We understand you're trying to setup Apple Pay, but you're being told you're in a country where it's not supported. We'd be happy to provide information to help you out.

Check to make sure your Apple ID country is setup correctly: Change your Apple ID country or region

Have a great day!