What Siri Can Do
It is important to say that developers can use Siri only within certain limits. Only Apple can "teach" Siri to do new things and developers can only use what is available to them.
There are three different Siri commands available for Debit & Credit. To use any of them, you need first to enable Siri in the advanced app settings.
Creating New Expenses as Bill Payments (Requires iOS 10.3 or watchOS 3.2)
Unfortunately, Siri does not understand commands to create new expenses but it knows how to pay bills. Debit & Credit is using bill payment commands to create new expenses in the app. There are two ways to use that command.
You can specify payee name and optionally account name right in a command. For instance, you could say "Pay my Comcast bill for $45 with my Citi account". Siri will find your existing Comcast payee, use its last used category (if any) and create a new expense on the Citi account.
Alternatively, you can just say "Pay my bill for $45". Once you do that, Siri will look for nearby payees. It will either use a payee that is close enough to you or will provide multiple payees to select from. If you don't have any payee locations saved in the app, your transaction will be created without a payee. Once a payee is selected, by default Siri will also choose the most appropriate category and account for that payee. You will be asked to confirm a transaction before it is saved.
Creating Transfers Between Accounts (Requires iOS 11 or watchOS 4)
This is a handy command when you want to record a transfer between two accounts in the app. Example: "Move $100 from my Citi account to my Visa account".
Checking Account Balance (Requires iOS 11 or watchOS 4)
You can ask Siri to display your account balance. Example: "What is the balance of my Visa account?". Two things to note:
1. Siri will not say your account balance, it will only display it. Unfortunately, this cannot be changed.
2. If there is an uncleared account balance, it will be displayed as a secondary account balance by Siri.
Settings for Siri
There are some advanced settings related to Siri and more specifically bill payments. You can find them in the advanced app settings.
Select Last Used Category - when creating a transaction, payee's last used category will be automatically selected.
Default Account - you can optionally designate an account to be used for Siri transactions.
Match Accounts With Payees - only accounts that you have previously used with a payee will be provided for selection.
Siri on Apple Watch
You can use Siri on the Apple Watch in the same manner as in iOS. However, you will need to open the watch app at least once to allow the app to download necessary records.
If You Don't Use Siri in English
Unfortunately, Siri can be a bit flaky when it comes to using it in languages other than English. If you have a problem with Siri, please don't hesitate contacting me. If there is indeed a bug in Siri, I will always report it to Apple (and hopefully they will fix it).