问题解决的关键是使用正确的版本号，这是在初始化All-in-One SDK时设置的。下面是一个Java代码示例，它使用正确的版本号并显示UPI为支付选项。

PaymentsClient paymentsClient = PaymentsClient.newBuilder()
                .setEnvironment(environment)
                .setGooglePayVersion(GOOGLE_PAY_VERSION)
                .build();

        IsReadyToPayRequest.TransactionInfo transactionInfo = IsReadyToPayRequest.TransactionInfo.newBuilder()
                .setTotalPriceStatus(TotalPriceStatus.FINAL)
                .setTotalPrice("10.00")
                .setCurrencyCode("USD")
                .build();

        IsReadyToPayRequest isReadyToPayRequest = IsReadyToPayRequest.newBuilder()
                .setTransactionInfo(transactionInfo)
                .addAllAllowedPaymentMethods(getAllowedPaymentMethods())
                .build();

        paymentsClient.isReadyToPay(isReadyToPayRequest)
                .addOnCompleteListener((task) -> {
                    try {
                        boolean result = task.getResult(ApiException.class);
                        if (result) {
                            // Payment is possible
                            // UPI is shown as a payment method
                        } 
               } 

请注意，关键部分是设置正确的GOOGLE_PAY_VERSION。在这个示例中，它被设置为“2019”（即版本“v2”）。