I haven't used the Intents for bill payment but the general pattern for SiriKit is that before you handle the user's request with a success/failure is that you can do some pre-processing (in a sense). This allows you to make sure you have everything you need to handle the bill payment where you make sure you have all the parameters you need (such as amount, account, and date to be paid).
In the WWDC video for messages, they show how Siri will come back to the user if extra information is missing, such as attempting to disambiguate between recipients in contacts with the same name. This is what you can try to look for/implement. Once any disambiguation is resolved and all parameters are me, you can then process the intent with a success/failure.