On a version before iOS 27, the automation doesn’t come with the shortcut, so you build it in Shortcuts. Then Arc reads each bank text on your iPhone and keeps the payment waiting in your inbox for a quick yes or no. It takes a few minutes.
Why “a”? Shortcuts needs something to look for, and almost every text has one.
The first time it runs, iOS asks: Allow “Arc · Bank SMS” to run actions from “Arc”? Tap Allow.
In Arc on your iPhone, go to Settings › Automatic logging › Bank texts and tap Send a test message. A sample bank text lands in your inbox.