Activity : activity instance
PaymentOption : Payment Option type e.g.PaymentOption.SAMSUNGPAY,PaymentOption.PHONEPE
PayUCustomBrowserCallback : this class provide callbacks
paymentOptionHash : Payment Related Details Hash
merchantKey : PayU Merchant Key
user_credentials : User credentials or use "default"
new CustomBrowser().checkForPaymentAvailability(Activity activity, PaymentOption paymentOption, PayUCustomBrowserCallback payUCustomBrowserCallback, String paymentOptionHash, String merchantKey, String user_credentials)