Android Chrome Webview access to Google Pay is not working
If you want to use Google Pay via a mobile app, you should use a native implementation, such as that offered by Stripe, or use a browser intent from your Android app to open the mobile Chrome browser
Just as a note, something similar happens with Apple Pay; Apple allows you to use a native implementation in an app, or web-based Apple Pay with mobile Safari or SFSafariViewController, but not more restrictive web views.