checkValidUPIId static method
Check if string is a valid Indian UPI ID
upiId - The UPI ID to validate
Returns true if UPI ID is valid
Implementation
static bool checkValidUPIId(String upiId) {
// UPI format: username@bankname or username@paytm, etc.
final upiRegex = RegExp(r'^[a-zA-Z0-9._-]+@[a-zA-Z0-9.-]+$');
return upiRegex.hasMatch(upiId);
}